The International Bar Association (“<span class="news-text_medium">IBA</span>”) Investment Arbitration Subcommittee has published its Report and Recommendations on Third-Party Participation in Investment Arbitration, addressing the growing use of third-party participation, or TPP, in investor-state dispute settlement (“<span class="news-text_medium">ISDS</span>”). The report focuses on participation by third parties such as amicus curiae and non-disputing treaty parties. Its stated aim is to encourage greater procedural clarity and consistency in how tribunals deal with TPP applications.
The IBA identifies TPP as an increasingly common feature of investment arbitration. Supporters argue that it can enhance legitimacy and transparency and assist tribunals in considering public interest issues. Critics, however, point to concerns about confidentiality, additional costs, delay, conflicts of interest and the principle of party consent.
The report adopts a practical approach. It recognises that TPP is now a reality in ISDS, but notes that tribunal practice remains inconsistent. The IBA’s empirical review, based on data collected up to 11 December 2024, identified 212 TPP applications across 135 investment arbitrations. Of these, 179 applications were made in ICSID arbitrations, with smaller numbers arising in proceedings before the SCC, PCA, ICC and in other ad hoc arbitrations.
The report also records substantial growth in TPP applications over the last two decades, especially between 2015 and 2019. By category, NGOs form the largest group of known applicants, representing approximately 54% of applicants whose identity is known. However, the European Commission is the most frequent individual applicant overall, accounting for nearly half of all applications. It is also the only known applicant in ICSID annulment proceedings.
The subcommittee identifies three main areas where greater harmonisation would be beneficial. First, it highlights the need for clearer procedural requirements, including disclosure obligations, opportunities for party comments and the extent of a tribunal’s power to invite third-party submissions on its own initiative.
Secondly, it addresses substantive requirements, including whether the proposed third-party submission provides a distinct perspective, whether the third party has a significant interest in the dispute and whether the submission concerns issues falling within the scope of the arbitration.
Thirdly, it considers necessary procedural safeguards, including timing, access to documents, confidentiality protections, formatting requirements, costs and measures to ensure that TPP does not impose an undue burden or disrupt the proceedings.
The report concludes that tribunals generally have authority to accept third-party submissions, even where the relevant investment treaty or arbitration rules are silent, by relying on their inherent procedural powers. However, it also notes continuing differences in how tribunals exercise that authority, particularly in relation to disclosure and whether tribunals may invite third-party submissions ex officio.
The IBA does not make a firm recommendation on costs, acknowledging that tribunal practice remains divided. It does, however, suggest that the approach to costs may differ depending on whether the third party applied voluntarily or was invited to participate by the tribunal. For counsel involved in ISDS proceedings, the report indicates that tribunals are likely to adopt a more structured approach to TPP applications. Parties should therefore be prepared to address the relevant procedural and substantive criteria at an early stage, including issues of scope, confidentiality, timing, burden and costs.
