What are amicus interventions for? Some provocations on non-disputing party submissions in international investment arbitration

1. Introduction

Amicus curiae participation in international arbitration has been historically seen as something of an interloper. Although there is broad agreement as to the potential benefits of non-disputing party participation for the integrity of the proceedings and the system, the perspective of non-disputing parties themselves and their approaches to the institution in light of its limitations are only rarely discussed. Yet, several actors interested in potentially appearing as non-disputing parties, or in facilitating this type of participation for other actors, have voiced their concerns. In a submission to the relevant stakeholders in the context of the UNCITRAL Working Group III Process concerning Investor-State Dispute Settlement Reform, several NGOs made the point that ‘amicus curiae is a shallow and narrow substitute for legal standing. Amici lack substantial procedural and substantive rights in ISDS proceedings. For example, they cannot receive direct compensation for legal injuries […]’.[1] In another such submission the point is made that amicus curiae participation is ‘not designed to grant effective voice or protection for actors whose rights are directly at stake in a dispute […]. At most, amicus is a mechanism to assist the tribunal in making its determination, and does not enable affected third parties to meaningfully intervene in order to protect their rights’.[2]

This contribution addresses the classic topic of the role of amicus curiae in international investment arbitration.[3] Its core focus is the purpose of the institution, at the theoretical as well as the practical level. In this contribution, I set out to make a series of provocations with a view to spark a reflection on this now venerable and yet hotly debated institution. Among these, the main one can be summarised as follows: whatever rules govern the admissibility of an amicus curiae intervention, whatever criteria are chosen in deciding on their admissibility, amici do not have an obligation to care much, if at all. While amici may, and ordinarily will, endeavour to assist the tribunal, they chiefly, and understandably, pursue their own agenda. This may include assuming roles and making arguments reserved for the parties, as well as using the institution politically rather than purely within the scope of a dispute settlement context. This is so because investment disputes, however reduced to a bilateral and legal affair, often unfold against the backdrop of a broader legal, political, or social conflict leaving certain actors (with no fault by the tribunal) with no recourse to a remedy.

These provocations have been sparked by my own reflections on practice. It is not customary to include the autobiographical in the analysis of important legal institutions, but I believe an exception is justified. This is a classic topic, and one in which I have only recently started to have a serious interest in. It is not so much that I considered it as a bit of an afterthought—an assessment which would not be completely unwarranted to an interested layperson reading sets of arbitration rules, especially in their early iterations. Rather, I must confess that my understanding of the institution was largely based on the scholarly debate surrounding it, and on the more doctrinaire side of it too. It was only after I was asked to participate in the writing of an amicus curiae submission in an investment case, on behalf of a number of actors, on which I will say more in a moment, that I become more interested in some of the more technical aspects connected to the institution. Of more immediate relevance, it is only after looking at how actors other than the parties and the tribunal looked at the institution of amicus curiae. In other words, the point I wish to make is that there are many ways to measure the purposes and successes of an amicus curiae intervention, and that it is a mistake not to take in due consideration the interests and objectives of the would-be intervener and the context of the dispute in the assessment of the successes and drawbacks of the institution.

To do so, this contribution proceeds as follows. After this introduction, in Part II, I outline the notion of amicus curiae intervention in investor-state arbitration, briefly discussing its main actors and intended purposes according to the orthodoxy. In Part III, I provide a summa of the approaches to the admission of amicus curiae interventions by investment tribunals. Finally, in Part IV, I endeavour to reverse the traditional perspective to invite consideration of the perspective of amici when assessing the merits and difficulties of the institution, before finally offering a conclusion.

Before delving into the substance, it is prudent to observe the following: it is not lost on the author that these are, to put it mildly, interesting times for third parties in international adjudication, the veritable flood of Article 63 interventions before the International Court of Justice being the most visible instance.[4] The roots and implications of these extraordinary times are addressed at length in the other excellent contributions in this symposium, and there is no need for the present essay to reproduce any of the points made there. Yet, it is prudent to remind the reader of a core distinction, however obvious it might be: amici curiae, too, may be labelled as third parties, but they are special third parties. They do not enjoy—with certain exceptions mostly concerning the role of states as non-disputing parties—direct and independent access to the jurisdiction by which they wish to be heard, even if they (or those they represent) suffer the political, economic, and social costs associated with the underlying investment relationship. Certain uses of the institution may therefore be seen as a form of revendication by parties which are routinely excluded in the political calculation giving rise to the economic relationship being arbitrated. Whether the institution is fit for purpose or whether the exclusion is wise are two different questions, which I do not propose to address.

Finally, and by way of clarification, throughout this essay I use the expression amicus curiae as largely equivalent to the far less catchy ‘non-disputing party’, with exceptions noted as needed.[5]

2. 2. Dramatis personae and rationale

Depending on whether one approaches the topic with deferential reverence or impatience, the topic of amicus curiae interventions in international investment arbitration may be seen as either a classic or something that has been done to death. Whatever the mindset, the result is often the same—one tends to assume that the basics are clear enough. I submit that this is not necessarily the case. In fact, there is something to be gained by some discussion of the basic building blocks of the institution. These are, at highest possible level of abstraction, the amicus (or amici) and the curia.

Little effort is needed to define the former: it is, by and large, simply a question of identifying the relevant adjudicator tasked with give a ruling on a specific matter. That this adjudicator should be a permanent adjudicatory body or a more transient—if not quite ephemeral—creature of consent matters little, in principle. That said, its nature cannot be seen as irrelevant at all, especially because the powers of the adjudicatory body concerned may be determined—for example, at the level of the rules governing its procedure, as agreed and set out by the relevant stakeholders—or otherwise developed in accordance with the mandate that it must, in the abstract, carry out. This question concerns the ‘ownership’ of the dispute resolution mechanism, a matter that, as the vast literature on courts domestic[6] and international has demonstrated beyond any possible doubt, is difficult to settle in the abstract, for even the most unfettered adjudicator will occasionally mimic the behaviour of more constrained bodies, yielding to party consent with a view to arriving to more conciliatory solution.[7]

The second question, that of the identification of the amici, is slightly more vexing. Obviously, it is possible, if historically rare, for this choice to be made specifically by the rules relating to the operation of the adjudicator concerned. Still, if provision for the institution of amicus curiae is made at all, there generally remains sufficient room for discretion by the adjudicator. It is true that some rules exist—and I shall return to them—which sanction the automatic eligibility of certain actors. Yet, in most cases, there is ample discretion for the tribunal to determine whether or not a specific actor may enjoy the status they desire. It is well accepted that international courts and tribunals may employ ‘general principles of law’ as a source of judicial procedure, and one may wonder whether and to what extent a principle of curia novit amicos, may exist and supplement the historically scant statutory provisions guiding the application of the institution. The result is the same, if through a different process, where the power to admit amici is grounded in the adjudicator’s inherent powers, the scope and rationales of which remain, of course, another matter on which reasonable minds may differ.[8]

Thus, question of the identity of the amici is largely a resolved through a value judgment concerning the function that they are going to play within the adjudicatory process. In this respect, the history of the institution of amicus curiae is, in many ways, a history of the debate on whether or not the relevant adjudicator should consider a broader range of considerations in reaching its decision, and it should not surprise, therefore, that the institution of amicus curiae should not be one of that is universally accepted, either at the domestic or international level.

At the definitional level, this tension is widely accepted: the Black’s Law Dictionary, the customary one-stop-shop for establishing the starting point of an adventure in semantics, clarifies that an amicus is at the level of common legal parlance. In its venerable second edition, it defines it as ‘[a] party that is not involved in litigation but gives expert testimony when the court asks. They can support public interest not being addressed in the trial’. The eight edition provides a more general definition, which is both more and less accurate: ‘[a] person who is not a party to a lawsuit but who petitions the court or is requested by the court to file a brief in the action because that person has a strong interest in the subject matter’.[9] These definitions are both reductive and inappropriate in the context of international dispute settlement broadly construed—and indeed discussions of the institution in the literature of the discipline reveal as much. Still, they broadly confirm that the idea underpinning the institution of amicus curiae is that there may be a need, or a desire, to assist an adjudicator so that it may best carry out its mandate, and that their presence in the dispute settlement process is largely ancillary.

Where this is conducive to justice being made, it is not difficult to accept, at the level of first principles, that actors which are neither formally nor—ideally—substantively parties to the dispute may have something to say, some form of specialised knowledge or illuminating perspective which, so long as neither the parties nor the relevant procedural rules stand in the way, may assist an adjudicator in providing the best possible result to the dispute before them. Inevitably, all of these words do a lot of work. The beauty of an outcome is in the eye of the beholder, and there is probably something to be said about the efficiency of a dispute settlement process unburdened by exogenous demands and materials not directly concerning the respective and mutual rights and obligations of the parties before it, especially where the form of adjudication in question remains one underpinned by the core principle of party consent.[10]

In investment arbitration, there is really no doubt that these are indeed disputes between an investor and a state. In this sense, and for all its monotrematous nature, this form of adjudication is straightforward and leaves little doubt as to between which parties the legal dispute ultimately is.[11] At the end of the day, the isolation and bilateralization of the dispute is not so much a legal fiction[12] as it is a function of the goal of depoliticization of the dispute.[13] In investment arbitration, this probably goes a step further than in general international law, which counts, among its pillars, the idea that any political dispute including legal elements can be reduced to those for the purposes of exercise of jurisdiction by a competent adjudicatory body.[14] In this sense, there is no question that there is no dispute between the would-be amicus and any of the parties to the legal dispute heard by the adjudicatory body.

This is not to say that the reality of the underlying conflict may not be more complex. There may be reasons why a dispute between two parties only may be problematic for actors other than those parties. An obvious point, when considering the intervention of State parties of multilateral treaties,[15] is that there may well be situations where there is an interest in the appropriate interpretation of the multilateral agreement concerned, pace the benefit of the principle of res inter alios acta, as well as of the cardinal principle whereby no rule of precedent applies in international law, borrowed by Article 59 of the ICJ Statute and believed, in practice, by none.[16] In other words, arbitral outcomes may be ‘subsidiary means’, but this qualification does little to placate the preoccupation of States, which may well want to kill a risky precedent before it snowballs into something uncontrollable. Law is, after all, non-ergodic.[17] The role of other actors may be equally concerned with the development of the law in a certain direction, or simply voice the concerns of interest groups which have a connection with the economic relationship in which the dispute finds its basis. These actors, it is essential to reiterate, do not enjoy discrete standing. Their participation to the dispute settlement process between the investor and the State is therefore functional to the realization of a more general concern (and must not be detrimental to the realization of the parties’ own interests).

This is where international tribunals—not necessarily those settling differences between investors and states—may engage in an appreciation of the interests of actors which are not parties to the dispute. This has been found to amount to an indication that international adjudication performs a public function, at least lato sensu. According to Chester Brown, even simply admitting an amicus curiae submission, especially in the absence of an express power to do so, indicates an ‘acceptance of broader functions in settling disputes and clarifying legal issues in a way that takes account of the views of other stakeholders potentially affected by the decision, rather than just the parties to the dispute’. Taking these reflections to the extreme, the frequency of amicus curiae participation signals the perception by those who try to take on this role of international adjudication as a ‘global public good’, as Joshua Paine masterfully puts it in an influential essay, and the acceptance of this role by the adjudicators themselves.[18] The extent to which this public function of international adjudication may be realised may then depend on the choices made by the parties in relation to the requirement set out in relation to the balance struck between the interests of the parties and the openness of the adjudicatory process in terms of transparency and participation of non-disputing parties.

3. Legal framework and practice

A cursory reading of the relevant procedural rules pertaining to the adjudication of investment disputes reveals trend going in the direction of a more granular regulation of the issue, largely following the progressive refinement of the requirements concerning the admission and use of amicus curiae submissions by investment tribunals. Some frameworks have been historically more permissive, though without making any express positive provisions, whereas others have appeared seemingly stricter.[19] As an example of the first kind, it is possible to recall the system operating under NAFTA. As is well known, NAFTA allowed for ‘submissions by States parties to the Agreement on a question of interpretation of this Agreement’,[20] but made no provision for submissions by other actors. In the aftermath of the Methanex case, which allowed one such submission,[21] the matter was further touched upon by the NAFTA Free Trade Commission, which further clarified that the ‘[n]o provision of [NAFTA] limits a Tribunal’s discretion to accept written submissions from a person or entity that is not a disputing party’.[22]

Similarly, ICSID rules, too, have undergone a striking evolution. While the jury is still out on whether the reform will amount to innovation, rather than simple codification of relatively well-established practices,[23] the textual innovation is undeniable. Thus, the 2006 rules innovated by finally providing that under Article 37(2), after consulting both parties, the Tribunal may allow a person or entity that is not a party to the dispute (termed as the ‘non-disputing party’) to file a written submission with the Tribunal regarding a matter within the scope of the dispute. The Tribunal’s discretion to allow such a submission hinged on several considerations: whether the submission could provide a distinct perspective or insight not offered by the disputing parties, its relevance to the dispute, and the non-disputing party’s significant interest in the proceedings. Additionally, the non-disputing party’s involvement must not disrupt the proceeding or unduly burden or unfairly prejudice either disputing party, ensuring that both parties had the opportunity to present their observations on the non-disputing party submission.

Some instances of application of these criteria have quickly become classics due to their attempt to clarify the relevant requirements. For instance, the Tribunal in Philip Morris v Uruguay allowed the participation of the Pan American Health Organization in the following terms:

Yet, there remains considerable discretion available to Tribunals in the decision of whether to allow the participation of an amicus curiae. The word ‘may’ in Article 37(2) of the 2006 rules can do quite a lot of work. Tribunals have made it clear that they will not necessarily accept these conditions as exhaustive,[25] and will also exercise discretion within the constraints of the requirements already articulated by the relevant rules. Thus, for example, Tribunals have been able to reject a petition to intervene because it did not fall within the scope of the dispute, though the reasoning in this context has been highly variable. An interesting example is the Eco Oro case. The petitioners had proposed to focus ‘on international law regarding human rights and particularly the right to live in a healthy environment’.[26] The Tribunal flatly rejected the petition as it found it both too generic and outside of the scope of the dispute. According to the Tribunal, this was so because

Similarly, tribunals have rejected petitions on the basis that they would not assist the Tribunal fully. In Odyssey Mining v Mexico, the Tribunal rejected (by majority, rather than unanimity) the would-be amicus submission insofar as it ‘ha[d] not demonstrated that [the Center for International Environmental Law] can provide assistance on matters not addressed by the parties or that the parties are unable to provide in this arbitration’.[28] The Tribunal also observed that

This discretion remains largely unfettered. The recent reforms of the relevant procedural rules do not seem to do much more than codify these trends.[30] Thus, the 2022 ICSID Arbitration Rules have expanded and detailed the framework for non-disputing party submissions. These rules now allow any non-disputing party to apply for permission to file a written submission, with requirements concerning requiring the application to be in the procedural languages of the proceeding. The Tribunal’s considerations in permitting such submissions have broadened to include not only the potential contribution of the submission to resolving factual or legal issues and its relevance to the scope of the dispute but also the non-disputing party’s interest in the proceeding, the entity’s identity, activities, organization, and ownership, and whether there is any financial or other assistance provided for the submission. This represents a significant shift towards transparency and the consideration of potential external influences on the proceedings. Furthermore, Rule 67 introduces procedural safeguards such as the right of the parties to make observations on the application, the imposition of conditions on the submission to prevent disruption, and a requirement for the Tribunal to issue a reasoned decision within 30 days after the last written submission on the application.[31] Similarly, the rather permissive setup developed under NAFTA has been further refined under the successor of that agreement, the USMCA, which provides very similar criteria for the admissibility of amicus curiae submissions.[32]

4. Reversing the perspective

For an adjudicator conscious of the extent of its function, jurisdiction, and mandate, these concerns may be answered with the term of art ‘tough luck’. After all, the adjudicatory mechanism in question is a but a creature of some sovereign parties’ agreement to set up a specific institutional framework and to grant access to it to specific actors, which are understood as the only parties to the dispute. It is not surprising that an adjudicator should want to police the ownership of the adjudicatory mechanism itself to reflect whatever choices have been made in its creation. Still, there is something to be said about the current state of affairs and the difficulties it creates for the would-be amici. In other words, the fact that actors affected by the dispute, where this term is less narrowly construed, should be denied party status or a forum in which to make their case might contribute to explain why the instrument of the amicus curiae is sometimes deployed and leveraged in the context of arbitration proceedings, in ways that push the boundaries of the institution as delineated through positive regulation and arbitral jurisprudence. In this connection, I offer the following three reflections.

The first has to do with information asymmetry. I have already outlined the requirement, also included in procedural rules, that commands that amici offer a distinctive perspective, a particular knowledge or insight that is different from that of the disputing parties. In the abstract, it is difficult to disagree with the proposition that common sensical allegations have no place in the courtroom, even assuming a broader mandate for the adjudicator than the one typical of investment arbitration tribunals. Yet, while the goal is admirable in principle, achieving it is easier in theory than in practice. The Eco Oro case, already mentioned above, offers an instructive example. In that case, the petitioners applied for permission to file a non-disputing party submission pursuant to both the applicable 2006 ICSID Rules and the relevant FTA being applied. They made their case by observing that ‘any submission they make will provide a ‘unique contribution to the resolution of factual, legal and policy issues within the scope of the dispute’. They however conceded that,

As already discussed, the Tribunal made short work of this application—unsurprisingly. It did so as follows.

Accordingly, the Tribunal does not find that the Petitioners have met even the most minimum requirements that would be needed to establish that issues of human rights, and particularly the right to live in a healthy environment, may be said to form a part of the scope of the dispute’. [34]
Admittedly, this is an extreme case. As far as the reader can tell, the petitioners’ case was likely too weak to be considered viable. Yet, as a question of principle, this case raises an important question: to what extent should the petitioners carry the blame for their failure to demonstrate that their contribution will be specific and distinctive when they do not enjoy unfettered access to the very information that might enable them to satisfy the test? Naturally, this is a broader challenge concerning the overall transparency of arbitration proceedings, but one can see how significantly it might impact the ability of would-be amici to apply for leave file a non-disputing party submission. In this connection, Rule 67 of the 2022 ICSID Rules appears to mitigate the problem where it provides that ‘[t]he Tribunal shall provide the non-disputing Party with relevant documents filed in the proceeding, unless either party objects’.[35]

It may be observed in this connection that the use of the word ‘shall’ in Rule 67(6) suggests a presumption in favour of disclosure, placing the onus on the parties to object if they wish to withhold documents from a non-disputing party. This language was settled upon after some debate during the amendment process. In its early phases, the International Institute for Sustainable Development (IISD) had criticized the proposed rules for shying away from the transparency standards of the UNCITRAL Rules and called on ICSID to ‘ensure higher standards of transparency’.[36] Similarly, remarks from Korea and Costa Rica reveal a general interest in facilitating non-disputing party access to case materials, with Korea proposing an explicit right for non-disputing treaty parties to request documents,[37] and Costa Rica asserting that a non-disputing treaty party’s participation ‘should not be limited by specific conditions imposed by the Tribunal’.[38] At a later stage, the EU argued for the use of the word ‘shall’ from an earlier draft, expressing concern that changing it to ‘may’, as it had been proposed, would ‘make it more difficult for a non-disputing party to access information that may be relevant for informing its submissions’.[39] Israel, conversely, sought to revert back to ‘may’ to vest the tribunal with discretion based on the particularities of each case, warning a mandatory approach ‘might have the unwanted effect of serving as an incentive for third parties to request involvement in a case as an opportunity to get access to information of the disputing parties’.[40]

Notably, the final text creates a presumptive duty of disclosure that can only be overridden by party objection. However, the precise temporal scope of this duty remains unclear from the rule itself: does it apply as soon as a non-disputing party files its application under Rule 67(1), or only after the tribunal grants leave to intervene under Rule 67(5)? A literal reading of the text clearly militates in favour of the second option—and therein lies the problem: it is not a given that a would-be amicus will be able to make a compelling case that it should be allowed to intervene, on the basis of the criteria discussed thus far, without having access to the relevant information. Thus, an argument could be made in favour of giving aspiring amici a meaningful opportunity to review the record before finalizing their request for leave to file a written submission. In its absence, one may perhaps look with more leniency to the position of non-disputing parties seeking to maximize their chances of participating effectively.

The second problem concerns the number of ‘clients’ and stakeholders behind an amicus submission. It is, of course, possible to have a veritable consensus surrounding the content and modalities of the submission, but chances are this will be difficult to achieve in practice, especially where the submission is brought on behalf of grassroots communities, it might be the case that a sub-optimal strategy will still be chosen. Where this has occurred, however, Tribunals have sometimes managed not to throw out the baby with the bath water.

An instructive case in this sense is GCM Mining v Colombia,[41] where tribunal allowed the Asociación Mutual de Mineros ‘EL COGOTE’—which represented communities of miners to make submissions on (i) the socioeconomic and cultural context of the mine, the municipality and the armed conflict, (ii) the history of the investment and (iii) the past and present reactions of the civilian population.[42] However, the Tribunal elected not to allow for the submission to deal with matters relating with all of other issues and, in particular, with questions concerning the domestic mining legislation. While the latter question clearly fell within the scope of the dispute,[43] it failed to meet the more exacting requirement of providing ‘particular knowledge or insight that is different from that of the disputing Parties’.[44] In its Order, the Tribunals expressed its doubts as to the ability of an association such as that of the would-be amici to assist it in relation to legal questions. Most importantly, however, it found suggested that its assistance would have been, in any event, redundant, as the matters in question had ‘already have been addressed by at least one Party’.[45]

It is worth observing that in the case in question the Respondent had not objected to COGOTE’s application to intervene and had in fact confirmed that it had a significant interest in the arbitration.[46] In other words, this appears to be a case where the Respondent and the amicus would have been on the same team. This is not always the case: it is possible that for the relationship between the would-be amicus and the Respondent to be characterised by a complete lack of coordination, or to be informed by outright animosity. In circumstances such as those, it is not possible for the would-be amicus to be certain that the arguments object of an intervention will be made by the Respondent—especially when such arguments may, in fact, be unfavourable to it.

Obviously, the precise details of these scenarios might be radically different in light of the type of actor seeking to intervene: a non-governmental organization representing a group of indigenous communities is not the same thing as, say, the European Union. Yet, that does not mean that the treatment of the issues will be too far apart: an interesting example is provided by Wirtgen v. Czech Republic,[47] one of the many cases affected by the Achmea issue relating to intra-EU investment disputes.[48] In that case, like in many others that followed, the European Commission intervened in order to, inter alia, raise the objection whereby the applicability of European Union law deprived the Tribunal of jurisdiction. Notably, not only did the Respondent not raise the objection, but it made it clear that it did not intend to join the Commission in raising them.[49] The Tribunal resolved the matter by acknowledging that while ordinarily it is not open to a non-disputing party to raise a defence of lack of jurisdiction, it could and should satisfy itself that it had jurisdiction, and do so ex officio.[50] In nearly identical circumstances, the Green Power v. Spain Tribunal cited Wirtgen to argue that it was on this basis and this basis alone that it was possible to give due consideration to the European Commission’s amicus brief.[51] In other words, consideration of the arguments made by an actor not entitled to make them was ultimately allowed through a flexible understanding of the Tribunal’s inherent power—and, more precisely, inherent jurisdiction—to determine its competence.

Thus, identifying the extent of the overlap between arguments made by the one party or the other can be challenging for a tribunal. Accordingly, it may be cautiously argued that tribunals should, in general, show leniency when confronted with submissions that purport to address issues that have already been covered or are likely to be covered by the disputing parties, and that they may, if necessary, rely on their procedural powers to do so.

The third and final point is that there may well be situations in which a would-be amicus has—to put it diplomatically—ulterior motives. To be clear, it is not a requirement for intervening as a non-disputing party that one should be happy with the current system of investor-state dispute settlement, even if it is not normally envisaged that would-be amici will use an opportunity to intervene in the proceedings as a chance to voice their discontent. In other words, there is something to be said about what may be termed the subtle art of getting thrown out, meaning that the an amicus curiae intervention may be planned not so much with the goal of assisting the Tribunal, but rather for the purpose of raising a point that the petitioner believes should be heard—with the implication that, if it is not heard, the dispute settlement mechanism may be less than ideal.

For a tribunal, these translate as questions of optics. In this respect, an instructive example is provided by Odyssey Mining v Mexico. In that case, the Center for International Environmental Law (‘CIEL’) and the Sociedad Cooperativa de Producción Pesquera Puerto Chale (‘Cooperativa’) had submitted a joint application for leave to file a non-disputing party submission, intending to address various points related to the environmental implications of deep-sea mining.[52] The Tribunal, again, made short work of the application.[53] In particular, it stated as follows:

In his dissent, Professor Philippe Sands lamented the rejection of the Request for Leave to file an amicus curiae brief. He argued that CIEL was

Similarly, the Cooperativa was ‘in a unique position to give a first-hand [sic] account and thus support or challenge the arguments of the parties’ and that not granting leave to intervene amounted to a decision not ‘to hear from a community that is directly affected by the outcome of the proceedings’. In his view, one such decision would ‘only serve to undermine perceptions as the legitimacy of these proceedings’.[56]

These remarks show that, in addition to the criteria outlined thus far in relation to the admissibility of an amicus curia intervention in investment arbitration, another may be developing. As put by Professor Sands in his dissent in Odyssey Mining, this might have to do with the need, incumbent upon arbitrators, to have regard to ‘the legitimacy of the final award in light of both (a) general legitimacy concerns in relation investment treaty arbitration, and (b) specific local community interests that are engaged by a particular case’.[57]

A position of this kind raises important questions: concerns about the legitimacy of investor-state dispute settlement have been voiced by a number of actors, including States, international organizations, and academics—perhaps the most vocal of all. They are, in other words, nothing new.[58] Empirical research has also provided solid evidence that arbitrators are sensitive to the backlash and mood changes of state actors, though less so to that of more diffuse public opinion.[59] It is comparatively rare for arbitrators to make the point expressly in their individual opinions, and even rarer for tribunals to acknowledge these concerns expressly and to incorporate them in their decision-making. Yet, there are some indications that this might be changing. Thus, in Glencore v Colombia (III), the Tribunal stated dealt with matters of transparency by observing that it was

This approach is to be commended—arguably, there is no harm in considering general legitimacy concerns, and it might in fact be best to do so transparently, as these two examples demonstrate. While this might initially be seen as patching a leaky boat with chewing gum, in the long run, it could prove to be a necessary step in the evolution of investment arbitration. By actively engaging with the concerns raised by amici, arbitrators can play a vital role in reshaping the investor-state dispute settlement system to better serve the interests of all stakeholders.

5. Conclusion

This contribution examined, through some provocations, the role and evolving dynamics of amicus curiae interventions in international investment arbitration. While amici aim to contribute distinct perspectives and insights, their ability to significantly influence proceedings is inherently constrained by procedural rules, the discretion of tribunals, and the intrinsic nature of their non-disputing status. Still—and this is my modest contribution to the debate—the existing normative framework and jurisprudential trends do not always explain what would-be amici endeavour to gain from their participation in the proceedings, and why they sometimes adopt strategies that do not necessarily appear to conform to what tribunals may find more appealing. In particular, I have singled out challenges inherent in information asymmetry; the diversity of stakeholders involved in amicus submissions and their expectations concerning the range of perspectives to be championed; and the potential for amici to pursue broader agendas or advocacy goals, which finds a reflection in a possibly developing need for arbitrators to take into account the interests of affected stakeholders to preserve the very legitimacy of the investor-state dispute settlement system.

* Lecturer (Assistant Professor) in Public International Law, King’s College London; Associate Director, Centre for International Governance and Dispute Resolution; Academic Fellow, The Honourable Society of the Middle Temple. I am grateful to Attila Tanzi, Gian Maria Farnelli, Ludovica Chiussi, and Brian McGarry for the fruitful discussion from which this piece has been developed. I am also grateful to Laura Knöpfel, Clara María López Rodríguez, and Michał Swarabowicz for excellent comments. All errors and oversights remain my own.

[1] T&E, CIEL, ClientEarth, SOMO – Reform options for ISDS.

[2] Submission to UNCITRAL Working Group III on ISDS Reform, contributed by Columbia Center on Sustainable Investment (CCSI), International Institute for Environment and Development (IIED), and International Institute for Sustainable Development (IISD) (15 July 2019).

[3] The topic is indeed a classic and much has been written on it. What follows is a bona fide attempt to list relevant writings on the topic, which the author has found helpful. K Gómez, ‘Rethinking the Role of Amicus curiae in International Investment Arbitration: How to Draw the Line Favorably for the Public Interest’ (2012) 35 Fordham Intl L J 510; A Wiik, Amicus curiae before International Courts and Tribunals (Nomos Verlag 2018); G Born, S Forrest, ‘Amicus curiae Participation in Investment Arbitration’ (2019) 34 ICSID Rev – Foreign Investment L J 626; H Chen, ‘The Role of Amicus curiae in Implementing the Human Right to Water in the Context of International Investment Law’ (2020) 29 Rev Eur, Comparative & Intl Env L 454; C Baltag, ‘The Role of Amici Curiae in Light of Recent Developments in Investment Treaty Arbitration: Legitimizing the System?’ (2021) 35 ICSID Rev – Foreign Investment L J 279; L Crema, ‘Testing Amici Curiae in International Law: Rules and Practice’ (2013) 22 Ital­ian YB Intl L 91; E de Brabandère, ‘NGOs and the ‘Public Interest’: The Legality and Rationale of Amicus curiae Interventions in International Eco­nomic and Investment Disputes’ (2011) 12 Chicago J Intl L 91; S Faccio, ‘Public Participation in Arbitral Proceedings’, in A Kent, E de Brabandère, T Gazzini (eds), Public Participation and Foreign Investment Law. From the Creation of Rights and Obligations to the Settlement of Disputes (Brill, Nijhoff, 2021) 283-331; A Kent, ‘The Principle of Public Participation in NAFTA Chapter 11 Disputes’ in H Kong, K Wroth (eds) The History, Experience and Prospects for Reform (CUP 2015); A Kent, E de Brabandère, T Gazzini (eds) Public Participation and Foreign Investment Law. From the Creation of Rights and Obligations to the Settlement of Disputes (Brill, Nijhoff, 2021); PJ Sands, R Mackenzie, ‘International Courts and Tribunals, Amicus curiae’ Max Planck Encyclopedia of Public International Law (January 2008) 1 available at <https://opil.ouplaw.com/view/10.1093/law:epil/9780199231690/law-9780199231 690-e8?rskey=UV3K3o&result=1&prd=OPIL>.

[4] See the proceedings in the case Allegations of Genocide under the Convention on the Prevention and Punishment of the Crime of Genocide (Ukraine v. Russian Federation: 32 States intervening).

[5] E Obadia, ‘Extension of Proceedings Beyond the Original Parties: Non-Disputing Party Participation in Investment Arbitration’ (2007) 22 ICSID Rev – Foreign Investment L J 349.

[6] M Shapiro, Courts: A Comparative and Political Analysis (U Chicago Press 1986).

[7] There is no need to rehash the usual remarks on adjudicators accepting constraints having bearing on the determination of the dispute, the usual exampla being the Taba arbitration. See Location of the Boundary Markers in Taba between Egypt and Israel (29 September 1988) 20 UNRIAA 1-118. For the more general proposition that even a permanent adjudicator may be conceived as a creature of consent and behave as such, see ex multis S Forlati, The International Court of Justice: An Arbitral Tribunal or a Judicial Body? (Springer International Publishing 2014).

[8] See C Brown, A Common Law of International Adjudication (OUP 2007) 70, 76 (observing that in doing so, ‘[m]any international courts also occasionally take account of broader community interests’).

[9] BA Garner, Black’s Law Dictionary (West 2010).

[10] On consent in international adjudication, see generally A Orakhelashvili, ‘Consensual Principle’, in Max Planck Encyclopedia of International Procedural Law (2020) available at <www.mpi.lu/mpeipro/>. See also PR Romano, ‘The Shift from the Consensual to the Compulsory Paradigm in International Adjudication: Elements for a Theory of Consent’ (2006) 39 New York U J Intl L and Politics 791; T Sparks, ‘Reassessing State Consent to Jurisdiction: The Indispensable Third Party Principle before the ICJ’ (2022) 91 Nordic J Intl L 216.

[11] On these taxonomical aspects, see A Roberts, ‘Clash of Paradigms: Actors and Analogies Shaping the Investment Treaty System’ (2013) 107 AJIL 45. On the question of the scope of the dispute and the role of the amicus in its determination see Methanex Corporation v. United States of America, UNCITRAL, Decision of the Tribunal on Petitions from Third Persons to Intervene as ‘Amici Curiae‘ (15 January 2001) para 29 (‘The Tribunal is required to decide a substantive dispute between the Claimant and the Respondent. The Tribunal has no mandate to decide any other substantive dispute or any dispute determining the legal rights of third persons. The legal boundaries of the arbitration are set by this essential legal fact. It is thus self-evident that if the Tribunal cannot directly, without consent, add another person as a party to this dispute or treat a third person as a party to the arbitration or NAFTA, it is equally precluded from achieving this result indirectly by exercising a power over the conduct of the arbitration’). See also, in the same sense, also Suez, Sociedad General de Aguas de Barcelona S.A. and Interagua Servicios Integrales de Agua S.A. v. Argentine Republic, ICSID Case No ARB/03/17, Order in response to a Petition for Participation as Amicus curiae (17 March 2006) para 13.ia

[12] This point has been examined thoroughly in the literature. See eg RY Jennings, ‘The Judiciary, International and National, and the Development of International Law’ (1996) 45 ICLQ 1, 11. For an early and quite far-sighted discussion of the same point, see also South West Africa Cases (Ethiopia v. South Africa, Liberia v. South Africa) Judgment [1962] ICJ Rep 319, Dissenting Opinion of Judge Morelli at 566-567 (‘Quant à l’opposition d’intérêts, il est bien vrai que, comme on le verra par la suite, un différend se trouve nécessairement dans un certain rapport avec un conflit d’intérêts (réel ou supposé). Mais le conflit d’intérêts non plus ne s’identifie pas avec le différend. En outre, un conflit d’intérêts peut bien exister sans qu’il y ait un différend correspondant.’)

[13] IFI Shihata, ‘Towards a Greater Depoliticization of Investment Disputes: The Roles of ICSID and MIGA’ (1986) 1 ICSID Rev 1; D Schneiderman, ‘Revisiting the Depoliticization of Investment Disputes’ (2010) 11 YB Intl Investment L and Policy 693.

[14] See H Lauterpacht, The Function of Law in the International Community (1st pbk. edn, OUP 2011) 161 et seq.

[15] See eg NAFTA Article 1128, discussed infra, Part II.B.

[16] HG Cohen, ‘Finding International Law, Part II: Our Fragmenting Legal Community’ (2011) 44 New York U J Intl L & Politics 1049, 1078 (‘The worst kept secret in international law is that international tribunals rely on precedent’). A clue that there might be some operation of precedent in international law may also be demonstrated by the late Judge Shahabuddeen’s celebrated study of the topic: see M Shahabuddeen, Precedent in the World Court (CUP 1996). I would be remiss if I did not mention my own empirical work on the topic: see N Ridi, ‘Approaches to External Precedent: Invocation of International Decisions in Investment Arbitration and WTO Dispute Settlement’, Adjudicating International Trade and Investment Disputes: Between Isolation and Interaction (CUP 2018); N Ridi, ‘The Shape and Structure of the ‘Usable Past‘: An Empirical Analysis of the Use of Precedent in International Adjudication’ (2019) 10 Journal of International Dispute Settlement 200; N Ridi, ‘‘Mirages of an Intellectual Dreamland‘? Ratio, Obiter and the Textualization of International Precedent’ (2019) 10 J Intl Dispute Settlement 361; N Ridi, ‘Rule of Precedent and Rules on Precedent’ in E de Brabandère (ed), International Procedure in Interstate Litigation and Arbitration: A Comparative Approach (CUP 2021). For other empirical perspectives see D Charlotin, ‘The Place of Investment Awards and WTO Decisions in International Law: A Citation Analysis’ (2017) 20 J Intl Economic L 279; W Alschner, D Charlotin, ‘The Growing Complexity of the International Court of Justice’s Self-Citation Network’ (2018) 29 Eur J Intl L 83.

[17] OA Hathaway, ‘Path Dependence in the Law: The Course and Pattern of Legal Change in a Common Law System’ (2000) 86 Iowa L Rev. 601; AK Bjorklund, BH Druzin, ‘Institutional Lock-in within the Field of Investment Arbitration’ (2017) 39 U Pennsylvania J Intl L 707.

[18] J Paine, ‘International Adjudication as a Global Public Good?’ (2018) 29 Eur J Intl L 1223.

[19] I do not address here the inclusion of specific rules concerning the participation of amici in the bilateral or multilateral agreement itself, though there are multiple examples. See eg Colombia-United States Trade Promotion agreement (adopted 22 November 2006, entered into force 15 May 2012) available at <www.italaw.com/sites/default/files/laws/ italaw11095_0.pdf>.

[20] NAFTA art 1128.

[21] Methanex Corporation v. United States of America, UNCITRAL, Decision of the Tribunal on Petitions from Third Persons to Intervene as ‘Amici Curiae‘ (15 January 2001) (‘The Tribunal considers that allowing a third person to make an amicus submission could fall within its procedural powers over the conduct of the arbitration, within the general scope of Article 15(1) of the UNCITRAL Arbitration Rules. The wording of the subparagraph numbered [2] of Article 15(1) suffices, in the Tribunal’s view, to support its conclusion; but its approach is supported by the practice of the Iran-US Claims Tribunal and the World Trade Organisation’).

[22] Statement of the Free Trade Commission on non-disputing party participation available at <https://2009-2017.state.gov/documents/organization/38791.pdf>.

[23] See eg the comment in C Schreuer, ‘ICSID Rules and Regulations 2022: Article-by-Article Commentary Edited by R Happ and S Wilske’ (2023) 24 J World Investment & Trade 976, 980. See also AR Parra, ‘The 2022 Amendments of the Regulations and Rules of the International Centre for Settlement of Investment Disputes: Change and Continuity’ (2022) 23 J World Investment & Trade 717; C Titi, ‘La Révision Des Règlements Du CIRDI (The Amendments to the ICSID Rules and Regulations)’ (2023) <https://papers.ssrn.com/abstract=4370383>.

[24] Philip Morris Brand Sàrl (Switzerland), Philip Morris Products S.A. (Switzerland) and Abal Hermanos S.A. (Uruguay) v. Oriental Republic of Uruguay, ICSID Case No ARB/10/7, Procedural Order No 4 (24 March 2015) para 27. See also eg Aris Mining Corporation (formerly known as GCM Mining Corp. and Gran Colombia Gold Corp.) v. Republic of Colombia, ICSID Case No ARB/18/23, Procedural Order No 10 Decision on Non-Disputing Party Application (31 August 2021) para 27.

[25] See eg Gabriel Resources Ltd. and Gabriel Resources (Jersey) v. Romania, ICSID Case No ARB/15/31, Procedural Order No 19 (7 December 2018) para 51. Admittedly, the Tribunal considered the wording of the Canada – Romania BIT (2009), which contained a provision concerning the admission of non-disputing parties directing the tribunal to consider ‘among other things’ several criteria, thereby lending support to the idea that the criteria themselves would not be exhaustive.

[26] Eco Oro Minerals Corp. v. Republic of Colombia, ICSID Case No ARB/16/41, Procedural Order No 6 Decision on Non-Disputing Parties Application (18 February 2019) at para 18.

[27] ibid para 28.

[28] Odyssey Marine Exploration, Inc on their own behalf and on behalf of Exploraciones Oceanicas S. de R.L. de C.V. v. United Mexican States, ICSID Case No UNCT/20/1, Procedural Oder No 6 Decision on the Application for Leave to File a Non-Disputing Party Submission (Amicus curiae) (20 December 2021) para 23.

[29] ibid.

[30] These developments are very much indebted to the UNCITRAL Rules on Transparency in Treaty-based Investor-State Arbitration (United Nations Commission on International Trade Law [UNCITRAL]) UN Doc A/RES/68/109 (16 December 2013) as well as to the United Nations Convention on Transparency in Treaty-based Investor-State Arbitration, New York (adopted 10 December 2014, entered into force 18 October 2017) 3208 UNTS I-54749.

[31] 2022 ICSID Arbitration Rules art 67 available at <https://icsid.worldbank.org/ sites/default/files/documents/ICSID_Convention.pdf>. Art 68 also introduces provisions for the participation of non-disputing Treaty Parties, allowing them to make submissions on the interpretation of the treaty at issue.

[32] See USMCA, Annex 14-D Mexico-United States Investment Disputes art 14.D.7 (‘Each submission shall identify the author; disclose any affiliation, direct or indirect, with any disputing party; and identify any person, government, or other entity that has provided, or will provide, any financial or other assistance in preparing the submission. Each submission shall be in a language of the arbitration and comply with any page limits and deadlines set by the tribunal. The tribunal shall provide the disputing parties with an opportunity to respond to such submissions. The tribunal shall ensure that the submissions do not disrupt or unduly burden the arbitral proceedings, or unfairly prejudice any disputing party.’)

[33] Eco Oro (n 26) para 18. See also In this sense, see also Energía y Renovación Holding, S.A. v. Republic of Guatemala, ICSID Case No ARB/21/56, Procedural Order No 3, Partial Dissenting Opinion of Prof. Raul Vinuesa on Non-Disputing Party Participation para 14 (‘Por otra parte, la documentación existente en el expediente al presente no posibilitaría conocer acabadamente, ni a las Partes ni al Tribunal, qué cuestiones podrían estar o no ‘dentro del ámbito de la controversia.‘E n consecuencia, la exclusión de ciertas situaciones invocadas por las Solicitantes implicaría que, una vez que se conozca con precisión cual es el ámbito de la controversia, el Tribunal debería definir nuevamente si las situaciones invocadas por las Solicitantes [y que prematuramente rechazó el Tribunal], se encuentran o no dentro de ese ámbito’).

[34] Eco Oro (n 26) at para 29.

[35] 2022 ICSID Arbitration Rules art 67. To the best of the author’s knowledge, no tribunal has yet had an opportunity to apply Rule 67 of the 2022 Rules, although over 20 cases are now pending where the updated rules are applicable. There have been news reports of a possible non-disputing party submission by Québec in Ruby River Capital LLC v. Canada, ICSID Case No ARB/23/5, which was filed in June 2023.

[36] Compendium of Comments by States on Working Paper # 2 available at <https://icsid.worldbank.org/resources/rules-amendments>.

[37] Compendium of Comments by States on Working Paper # 3 available at <https://icsid.worldbank.org/resources/rules-amendments>.

[38] ibid.

[39] Compendium of Comments by States on Working Paper #5 available at <https://icsid.worldbank.org/resources/rules-amendments>.

[40] ibid.

[41] Gran Colombia Gold Corp. v. Republic of Colombia, ICSID Case No. ARB/18/23.

[42] Gran Colombia Gold Corp. v. Republic of Colombia, ICSID Case No. ARB/18/23, Procedural Order No 10 Decision on Non-Disputing Party Application (31 August 2021).

[43] ibid para 35.

[44] ibid para 36.

[45] ibid para 33.

[46] ibid para 24.

[47] Jürgen Wirtgen, Stefan Wirtgen, Gisela Wirtgen and JSW Solar (zwei) GmbH & Co. KG v. Czech Republic, PCA Case No 2014-03.

[48] CJEU (Grand Chamber), Slowakische Republik (Slovak Republic) v. Achmea BV, Case C-284/16 Judgment (6 March 2018). With special reference to the Energy Charter Treaty, see also CJEU (Grand Chamber), Republic of Moldova v. Komstroy LLC, successor in law to the company Energoalians, Case C-741/19 Judgment (2 September 2021).

[49] Jürgen Wirtgen, Stefan Wirtgen, Gisela Wirtgen and JSW Solar (zwei) GmbH & Co. KG v. Czech Republic, PCA Case No 2014-03 Final Award (11 October 2017) para 249.

[50] ibid para 250.

[51] Green Power Partners K/S and SCE Solar Don Benito APS v. Kingdom of Spain, SCC Case No V2016/135 Award (16 June 2022) para 126.

[52] Joint application seeking authorization for the Sociedad Cooperativa de Producción Pesquera Puerto Chale S.C.L. and the Center for International Environmental Law to act as amicus curiae in Arbitration proceedings Odyssey Marine Exploration, Inc. v. United Mexican States (ICSID Case No. UNCT/20/1) (12 October 2021) available at <www.ciel.org/wp-content/uploads/2022/02/Amicus-Curiae-application-for-leave-and-submission-of-CIEL-and-the-Cooperativa-Puerto-Chale-2.pdf> . See also ‘CIEL and Fishing Cooperative File Amicus Brief in Odyssey Marine Exploration v. Mexico’ (Center for International Environmental Law) <www.ciel.org/news/ciel-and-fishing-cooperative-file-amicus-brief-in-odyssey-marine-exploration-v-mexico/>.

[53] Odyssey Marine Exploration, Inc. v. United Mexican States, ICSID Case No UNCT/20/1, Procedural Order No. 6 Decision on the Application for Leave to File a Non-Disputing Party Submission (Amicus curiae) (20 December 2021).

[54] ibid paras 22-23.

[55] Odyssey Mining, supra n53, Dissenting Opinion of Professor Philippe Sands para 3.

[56] ibid para 5

[57] ibid para 1.

[58] The landmark study in this sense is SD Franck, ‘The Legitimacy Crisis in Investment Treaty Arbitration: Privatizing Public International Law through Inconsistent Decisions’ (2005) 73 Fordham L Rev 1521; See also, among many others, CN Brower, SW Schill, ‘Is Arbitration a Threat or a Boom to the Legitimacy of International Investment Law’ (2008) 9 Chicago J Intl L 471; A Stone Sweet, F Grisel, The Evolution of International Arbitration: Judicialization, Governance, Legitimacy (OUP 2017).

[59] See Malcolm Langford and Daniel Behn, ‘Managing Backlash: The Evolving Investment Treaty Arbitrator?’ (2018) 29 Eur J Intl L 551.

[60] Glencore International A.G. v. Republic of Colombia (III), ICSID Case No ARB/21/30, Procedural Order No. 2, Procedural Order No. 2 (26 January 2024). This procedural order was published after the submission of the article, and incorporated at the proofing state.