Moonlighting and Multiple Hatting in International Law

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Luca Brocca

Just Access Representative to the UN Convention Against Corruption

In the last sixty years, there has been a remarkable increase in international courts and tribunals established by states through international or supranational bodies.[1] These institutions have been entrusted with the task of adjudicating cross-border matters, resulting in what has been called the “legalization of world politics”.[2] These various courts and tribunals have not only helped to make world politics an area of adjudication, but they have also had an impact on people’s everyday lives.

At the same time as the number and influence of international courts and tribunals have grown, increasing attention has been paid to the harmonizing activities of international law aimed at ensuring the independence of the judiciary at both the national and international levels. This focus has materialized in various international instruments, such as the UN Basic Principles on the Independence of the Judiciary (1985), the Recommendation of the Committee of Ministers of the Council of Europe to the Member States on the Independence, Efficiency and Role of Judges (1994), the Council of Europe’s European Charter on the Statute for Judges (1998), as well as the Bangalore Principles of Judicial Conduct (2002) together with their commentaries.

This blog post aims to analyze the moonlighting and multiple-hatting of international judges and investment arbitrators. It will do so by highlighting the importance of ensuring the independence and accountability of international judges. The challenges faced by investment arbitrators in particular underscore the need for clear guidelines and ethical standards. This blog post will show that by addressing these challenges and promoting a culture of transparency and accountability, the international community can strengthen the integrity and legitimacy of the global judicial system. 

Arbitrators, because of their special role, face some special ethical issues that cannot be equated with those of judges, auditors, or lawyers. There are no central mechanisms for setting ethical rules, which makes their roles unique. Investment arbitration is at the forefront of the arbitration profession and regularly confronts arbitrators with complex ethical dilemmas, particularly with respect to multiple conflicts of interest. However, there is no consensus on how these ethical obligations should be operationalized.[3]

The expansion of international arbitration has led to increased scrutiny, particularly in the area of investment arbitration. The perception of investment arbitration as an “obscure legal system that lets corporations sue countries”[4] has raised public concern. In response, the arbitration community has engaged in discussions, empirical research, and efforts to reaffirm the legitimacy of international investment arbitration.

In various legal contexts, the issue of international adjudicators’ external activities while serving on international tribunals has already been addressed.[5] However, the practical application of the formal parameters to ensure independence has sometimes been laxer than intended.[6] The ICJ in particular has grappled with its approach to incompatibility, with interpretations of “relative incompatibility” and “absolute (functional) incompatibility” evolving over time.[7] While the statute prohibits members of the Court from acting as agents, counsel, or advocates in any case,[8] some judges have been permitted to participate in other outside activities.

About five years ago, former ICJ President Judge Abdulqawi Yusuf addressed the Court’s decision to regulate the “extrajudicial activities” of ICJ judges.[9] This decision prohibits sitting ICJ judges from accepting new appointments as arbitrators in investor-state proceedings, and they can participate in inter-state court proceedings only in exceptional circumstances.

While President Yusuf justified this decision by citing the Court’s “ever-increasing workload,”[10] it was arguably taken in response to a legal and ethical dilemma that critics of investment arbitration have referred to as “moonlighting”[11]: the situation in which acting ICJ judges perform other functions in addition to their full-time employment at the Court, including serving as investment arbitrators or as members of annulment panels at the International Centre for Settlement of Investment Disputes (ICSID). Recent statistics show that around 20 ICJ judges have been involved as arbitrators in investor-state dispute settlement (ISDS) in at least 90 cases.[12] One of the reasons for this practice is that ICJ judges have economic incentives for serving as arbitrators. As ICJ judges, they receive an annual salary of around $173,000 (as of 2016)[13] plus allowances and a pension after retirement. In contrast, arbitrators are generally paid per hour or per day, resulting in different fees depending on the duration and complexity of the cases.[14]

The previously mentioned decision to exclude current ICJ judges from serving as arbitrators in investor-state cases was intended to place the judges’ impartiality and independence beyond reproach. However, this was only a solution to one of the dilemmas that investment arbitrators face in the course of arbitration proceedings – the others include issue conflicts, such as multiple hatting. This refers to the situation where an arbitrator in one case acts as an independent expert in another case.

The recent EU texts on ISDS all address multiple hatting to some extent, which is undoubtedly a positive development compared to thousands of BITs that do not explicitly address the issue of role reversal.[15] However, the EU texts do not address all of the potentially problematic facets of multiple hatting, and it is therefore necessary to consider their shortcomings and propose mechanisms by which they could be improved.

Two factors complicate the resolution of this dilemma in investment arbitration: first, unlike regulations of judicial conduct in national legal systems, there is a multiplicity of rules that originate in different legal systems and result in different legal hierarchies that could shape or guide the actions of investment arbitrators. Second, unlike in national legal systems, there is no body at the international level comparable to a national judicial council that could clarify the possible contradictions between such rules, leaving arbitrators with considerable leeway.[16]

Addressing the ethical challenges faced by investment arbitrators is critical, given the potential impact of their decisions on global affairs. The multiplicity of rules and the lack of a global authority to harmonize and clarify potential contradictions make this task complex.

For these reasons, several scholars have proposed the creation of a new code of conduct in this area to prevent further fragmentation of norms and promote ethical standards.[17] This would provide a comprehensive approach that takes into account the various “sources of duty” that govern the conduct of arbitrators. Codes of conduct for judges and arbitrators should be rigorously enforced, and internal case management systems should be established to ensure that ethical standards are met.

In addition, a proactive policy of publicly communicating neutral information can help dispel misunderstandings and promote more transparency in the arbitration process.[18] By informing the public about the decision-making process and the factors considered in reaching a verdict, international courts can increase their legitimacy and credibility.

In conclusion, it is now necessary to enshrine the principles of independence of the international judiciary in legislative form, also including issues of impartiality, conduct, and diligence in order to ensure, in concrete terms, the best possible level of guarantees.[19] In addition, international courts and tribunals should adopt more transparent and formal procedures to govern judicial accountability, particularly through codes of conduct, internal case management systems, and more proactive policies of public disclosure of neutral information.

Addressing these challenges is essential to preserve the reputation and legitimacy of the ICJ as the highest authority of international law.

[1] Mahoney, P. (2008). The international judiciary independence and accountability. Law and Practice of International Courts and Tribunals, 7(3),313-350.

[2]Goldstein, J., Kahler, M., Keohane, R. O., & Slaughter, A.-M. (2000). Introduction: Legalization and World Politics. International Organization, 54(3), 385–399.



[5] Shetreet S (2003) Standards of conduct of international judges: outside activities. Law Pract Int Courts Tribunals 2:127–161

[6] Katia Fach Gomez, Key Duties of International Investment Arbitrators: A Transnational Study of Legal and Ethical Dilemmas, New York, Springer, 2019

[7] Giorgetti C (2015) The challenge and recusal of judges at the International Court of Justice. Brill, Leiden, pp 3–33

[8] Article 17. ICJ Statute (1946)

[9] Speech by H.E Mr. Abdulaawi A. Yusuf. President of the ICJ, on the Occasion of the Seventy-Third Session of the UN General Assembly. 25 October 2018.

[10] Ibid.

[11] Prieto Munoz, J. (2020). Katia Fach Gómez, Key Duties of International Investment Arbitrators: A Transnational Study of Legal and Ethical Dilemmas, New York, Springer, 2019



[14] Ibid.

[15] i.e. CETA, EU-Singapore IPA, EU-Vietnam FTA

[16] Prieto Munoz, J. (2020). Key duties of international investment arbitrators: transnational study of legal and ethical dilemmas. Leiden Journal of International Law, 33(3), 819-[ii]

[17]  Katia Fach Gomez, Key Duties of International Investment Arbitrators: A Transnational Study of Legal and Ethical Dilemmas, New York, Springer, 2019

[18] Mahoney, P. (2008). The international judiciary independence and accountability. Law and Practice of International Courts and Tribunals, 7(3),313-350.

[19] Ibid. For a recent attempt see the Draft code of conduct for judges in international investment dispute resolution and commentary, A/CN.9/1149, for the UNCITRAL fifty-sixth session in Vienna in July 2023. To follow the evolving practice and the still unsatisfactory range of proposals, see

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Moonlighting and Multiple Hatting in International Law