This article examines the 2024 decision in Ukraine v. Russia (PCA Case No. 2019- 28), in which a United Nations Convention on the Law of the Sea tribunal upheld challenges to two arbitrators – Donald McRae and Rüdiger Wolfrum – due to their prior support for a 2022 L’Institut de Droit International’s Declaration condemning Russian aggression. The tribunal found that the involvement of these arbitrators raised justifiable doubts as to impartiality, highlighting the expanding role of perceived bias in inter-State arbitration. In a forceful dissent, Christopher Greenwood cautioned against conflating general academic expression with prejudgment, emphasizing the need for judicial restraint and procedural integrity. This note explores the tribunal’s reasoning, dissenting views, procedural standards, and comparative jurisprudence, including Canfor v. USA and Perenco v. Ecuador. It reflects on the growing tension between academic freedom and arbitrator impartiality, evolving disclosure norms, and the risk of strategic challenges in politically sensitive disputes, with implications for the future practice of international adjudication.

I. Introduction
II. Procedural Context and the Challenge Mechanism
    A. Procedural Background and Basis of the Challenges
III. The Majority Decision: Impartiality Standardand Timeliness
    A. The Majority’s Reasoning: Impartiality Standard,Timeliness, and Justifiable Doubts
IV. Greenwood’s Dissent: Judicial Restraint and theRisk of Overreach
    A. No Prejudgment of Issues
    B. Timeliness and Good Faith
    C. Underlying Policy Concerns
V. Canfor v United States and Perenco v Ecuador:A Comparative Perspective
    A. Canfor Corporation v. United States of America
    B. Perenco Ecuador Limited v. Republic of Ecuador
VI. Reconceptualizing Arbitral Governance:The Ukraine v. Russia Legacy and Its SystemicImplications
    A. Enhanced Disclosure Obligations: Reconciling AcademicFreedom and Procedural Integrity
    B. Expanding the Role of Context in Bias Assessment:The “Reasonable Observer” Standard Revisited
    C. Procedural Strategy, Timeliness, and the Risk of TacticalChallenges
    D. Consequences for Tribunal Composition, Party Autonomy,and Institutional Design
    E. Precedential Value and Future Development ofInternational Arbitral Jurisprudence
VII. Conclusion

• Chao Wang(Professor of International Law at the University of Macau Faculty of Law)