Might or Right? The Prospect of an ICJ Advisory Opinion on the Security Council Veto

The United Nations Security Council (“SC”) veto has once again become a focal point of debate. Russia’s invasion of Ukraine and paralysis over the situation in Gaza have revived a familiar concern: the SC’s primary responsibility for maintaining international peace and security appears ill served when one permanent member (“P5”) can unilaterally block even minimal action in response to mass atrocity crimes.

For decades, discussions about constraining the veto remained largely theoretical. This has shifted. In April 2022, the General Assembly (“GA”) adopted Resolution 76/262 (the “Veto Initiative”), which requires the GA to meet after a veto has been cast in the SC. Although this does not affect P5 powers, it reinforces the idea that veto use must be justified. Since then, the debate has intensified. Notably, in a speech before the GA, Slovenia called for the Assembly to seek an advisory opinion from the International Court of Justice (“ICJ”) “on the legal limitations to casting a veto in [concerning] situations involving widespread atrocity crimes such as genocide and crimes against humanity since their prevention and punishment are considered as peremptory norms of international law”.

This post first outlines recent efforts to constrain the veto and the emerging argument that some exercises of the veto may breach binding norms of international law rather than merely offend political expectations. It then turns to the proposal for an ICJ advisory opinion and considers if this could meaningfully recalibrate the normative environment in which the veto operates.

Slovenia’s Proposal to Rein in the P5 Veto: Old Wine in New Bottles?

In her address to the GA during its 80th session in September 2025, the Slovenian president delivered a pointed critique of the apparent erosion of multilateralism, asserting that the SC’s paralysis, the weakening of international courts, and states’ withdrawals from key treaties have threatened the integrity of the multilateral legal order. The speech advanced a broader normative agenda: revitalising the Pact for the Future through a proposed “Global Forum for the Future”, a core part of which is the demand for accountability for atrocity crimes. Rejecting multipolar power politics, the Slovenian president called for inclusive, law-centred multilateralism in which human dignity, legal responsibility, and institutional reform are indispensable to the survival and credibility of the international system.

Most notably, the Slovenian president challenged the prevailing understanding of SC authority in her speech, asserting that the SC is not and must never be positioned above international law. This argument hinges on the hierarchy of norms: if the prohibitions against genocide and crimes against humanity are accepted as jus cogens norms, then their peremptory character necessarily constrains all state conduct, including the exercise of the veto by the permanent members. The speech, as such, reframes the use of veto in atrocity crimes not as a political prerogative but as a legal question of compatibility with higher norms. Recognising the lack of progress in political reform of the SC, Slovenia proposed an initiative to seek an advisory opinion of the ICJ on the legal limitations to casting a veto in the SC concerning atrocity crimes.

Slovenia’s proposal to rein in the P5 veto does not stand alone. Over the past decade, UN member states and groups have advanced different attempts to reshape the veto. The most prominent of these is the Veto Initiative, which was co-sponsored by nearly 80 countries. The Initiative created a new procedure requiring GA’s President, when a veto is cast in the SC, to convene a formal meeting within 10 working days in which all UN members can discuss the vetoed issue and where the P5 member who used its veto is expected to explain its reasons. The SC is also “required” (albeit in non-binding terms) to submit a special report to the GA on the veto. While these are non-binding obligations, they create political friction around veto use and establish a forum for scrutiny.

Alongside the Veto Initiative, two attempts at voluntary restraint have sought to change the expectations surrounding atrocity-related voting. The first attempt is by the Accountability, Coherence and Transparency (“ACT”) group, a group of 27 states led by Liechtenstein, who launched a “Code of Conduct regarding Security Council action against genocide, crimes against humanity or war crimes” in 2015. This Code calls on all SC members, P5s and elected (“E10”) alike, not to vote against (i.e., not to veto) any “credible” draft resolution aimed at preventing or halting mass atrocity crimes. Since then, the Code has been endorsed by more than 130 countries and two P5s (France and the UK).

The second is the 2015 political declaration spearheaded by France and Mexico, urging the P5 to voluntarily suspend its use of the veto in cases of mass atrocities. This initiative frames the veto not as a privilege but as a “responsibility” that should never impede action to stop atrocity crimes. Although over 100 states have backed the France–Mexico declaration, none of the other P5 other than France have endorsed it.

Besides reform attempts put forward by states, reform proposals launched by The Elders, a “group of global leaders working to promote peace and human rights”, have, inter alia, called for the P5 to pledge “not to use, or threaten to use, their veto” in crises in which genocide or other mass atrocities are committed or threatened “without explaining, clearly and in public, what alternative course of action they propose, as a credible and efficient way to protect the populations in question”. In addition, prior to the work of the Elders, a related initiative had been advanced by former UN Legal Counsel Hans Corell, which called on P5s to “agree not to use their veto unless their most serious direct national interests were affected”.

Taken together, these initiatives situate Slovenia’s proposal within an already crowded reform landscape marked by broad agreement on the undesirability of the use of the veto in atrocity situations but persistent disagreement on how to respond institutionally. The question that follows is, therefore, not whether restraint enjoys normative support, but whether that support can be mobilised into a General Assembly request for an advisory opinion.

Mobilising the General Assembly Around the Veto Advisory Opinion

While no states have explicitly supported Slovenia’s initiative for an advisory opinion, Slovenia’s proposition that the use of the veto must be restrained is widely echoed by many states. During the 47th plenary meeting of the GA this November, in which the fourth general debate on the use of the veto agenda item was convened, more than 67 states reflected on the use of the veto and called for further action. Liechtenstein, on behalf of 56 states committed to the Veto Initiative, underscored that the GA has a residual responsibility to act when the SC is incapacitated by the veto, particularly when that veto obstructs responses to threats to peace.

Brazil, reflecting on existing efforts made by the Assembly, highlighted that the Veto Initiative “has not fulfilled its purpose of constraining permanent members to cast their vetoes in the SC”, rather it “gave the permanent members another platform to come before the entire membership to present yet again the reasons why they vetoed a resolution”. Luxembourg, on behalf of the Benelux states, expressed that “the Assembly can and must be more than a forum for expressing statements of principle”, as highlighted by precedents where the GA pursued alternative mechanisms to uphold international peace and security – such as requesting the ICJ to give an advisory opinion, creating true and just mechanisms and institutions, and supporting humanitarian actions.

In this context, there is consensus among most states that existing efforts are insufficient and that member states must take further steps to expand the GA’s proactive role in response to the SC’s use of the veto.

Indeed, during the fourth general debate on the use of the veto, many states converged on the notion of “no veto in atrocity crimes”, even as they disagreed on the mechanism. Slovenia itself framed the veto as something that “should never stand in the way of urgent action against genocide, crimes against humanity or war crimes” and links this to its advisory opinion initiative. In this context, several states have noted the exercise of vetoes regarding Gaza and Ukraine, which may serve as motivating factors for supporting a request for an advisory opinion.

The main headwinds will inevitably come from the P5s. Russia, for example, views the veto debates as politicised and performative, alleging the discussion has not “added value” and that veto-related proposals are tabled to “compromise an opponent”. This provides a preview of the difficulties to come: requesting an advisory opinion can be construed as lawfare and, even, selective justice. Furthermore, obstacles may arise from states such as India and Egypt, which prefer more structural reforms to the SC and may worry that an advisory opinion from the ICJ could distract from intergovernmental negotiations on SC reform. Finally, even sympathetic states may abstain to avoid antagonising one or more P5s, because an advisory opinion, albeit non-binding, can be politically costly.

Nevertheless, two recent precedents are instructive in how the movement for an advisory opinion on the P5 veto can win political acceptance within the GA. In 2023, the GA adopted, by consensus, a resolution requesting an advisory opinion on the obligations of states with respect to climate change. This milestone consensus was arguably possible because the question was framed to concern the legal obligations of all states, rather than as a finding against particular states, making it easier for many delegations to support it without necessarily politicising the matter or “taking sides”.

However, this is not to say that politicised and controversial questions cannot rally majority support. In December 2024, the GA voted to request another advisory opinion – this time focused on Israel’s obligations to facilitate humanitarian assistance and basic services involving the UN, other organisations, and third states. The resolution, led by Norway, was adopted with 137 votes in favour. This shows that a strong majority can be assembled at the GA even for highly polarising issues, albeit with substantial abstentions and organised opposition.

Turning to Slovenia’s initiative, a simple majority appears realistic if the resolution is framed as a general Charter interpretation and/or a question of legal obligation. In practice, the best campaigning theory that Slovenia can adopt is such that most states agree politically that vetoes should not be exercised in relation to atrocity crimes. What is needed, however, is legal clarity on what international law and the Charter already require.

Are There Legal Limits on the Veto?

Much of the consternation about the veto stems from the fact that the Charter cannot realistically be amended to change the veto. According to the Charter’s Article 108, such an amendment would require ratification by the P5. Deadlock on formal SC reform is therefore certain. Yet, as vetoes proliferate in situations involving grave violations of international law, the idea that the veto itself may be constrained by the Charter and by other binding norms has gained traction.

Most significantly, a growing body of scholarship proposes that some uses of the veto are inconsistent with international law. The central contention is that P5s remain bound by peremptory norms and by obligations arising from treaties such as the Genocide Convention and the Geneva Conventions. A veto that enables or perpetuates serious violations of jus cogens would, on this account, be legally impermissible. Scholars arguing along these lines point to the duty of states not to aid or assist serious breaches of peremptory norms, reflected in Article 41 of the ILC’s Articles on State Responsibility. A veto that blocks action intended to halt an ongoing genocide or widespread war crimes may constitute such aid or assistance. The ICJ itself recognised in its 2004 Wall (para. 159) and 2019 Chagos Archipelago (paras. 177 and 182) advisory opinions that states have an obligation to refrain from aiding violations of peremptory norms. In this reading, the Charter should not be interpreted in a manner that permits P5s to facilitate the continuation of genocide or other atrocity crimes through a veto.

Treaty obligations reinforce this argument. Article I of the Genocide Convention imposes a duty to prevent genocide. A veto used to disable UN action designed to prevent or suppress genocide sits uneasily with that obligation. The same applies to Common Article 1 of the Geneva Conventions, which obliges its High Contracting Parties to “undertake to respect and ensure respect for the Convention in all circumstances” (emphasis added). A related constraint is in the Charter itself. Article 24(2), which states that the SC “shall act in accordance with the ‘Purposes and Principles’” of the UN, has been central to many scholarly theories of how to limit the SC’s powers. Similarly, Article 27(3) requires a party to a dispute to abstain from voting on decisions under Chapter VI. This provision, however, is often ignored. For example, Liechtenstein and Bulgaria have warned that the implementation of Article 27(3) has been lacking. Japan has likewise stressed the need for states to fully adhere to all provisions of the Charter, including Article 27(3).

Moreover, from an institutional viewpoint, the SC is not above the law. The ICJ made this clear in its 1948 Conditions of Admission (p. 64) advisory opinion, in which it held that the SC “bound to observe the Charter”, just like any individual member state is. Judge Fitzmaurice echoed this sentiment in his dissenting opinion in the 1971 Namibia advisory opinion (para. 115). Similarly, the ICTY held in the 1995 Tadić case that the SC is subject to certain constitutional limitations under the Charter, even though its powers thereunder may be broad. In this regard, judicial decisions and opinions by individual judges have consistently affirmed that the SC’s discretion (i.e., veto) is constrained: it must comply with the Charter, cannot validly act ultra vires, and is not legibus solutus (unbounded by the law). The corollary of this institutional argument is that, since all member states are themselves bound by jus cogens, they cannot confer on the SC authority to act contrary to such norms, or else international organisations may (at least theoretically) be used by states to bypass jus cogens obligations.

None of this removes the grey zones. The causal link between a veto and the continuation of atrocities is contestable. Still, a significant number of states now proceed on the premise that the veto is framed and limited by international law, and that the SC is not a “law free space”. Once that premise is accepted, a further question inevitably arises: if such limits exist, should the ICJ be asked, through an advisory opinion, to clarify their content and implications for SC practice?

What Could an ICJ Advisory Opinion on the P5 Veto Achieve?

The GA may request an advisory opinion from the ICJ on “any legal question” pursuant to the Charter’s Article 96. The ICJ has repeatedly affirmed that the presence of political dimensions does not deprive a question of its legal character. The 2010 Kosovo (para. 26), 1996 Nuclear Weapons (para. 13), and 1971 Namibia (para. 29) advisory opinions all confirm the ICJ’s willingness to offer guidance on matters that lie at the junction of law and international politics.

A request concerning legal limits on the veto would need careful framing. It should instead ask in general terms whether, and under what conditions, the exercise of the veto is consistent with the Charter and with binding norms of international law. The GA could, for example, ask the ICJ to clarify the relationship between Article 27 of the Charter and states’ duties to prevent genocide and ensure respect for humanitarian law, or the proper interpretation of Article 27(3) in contemporary conflicts. Such an advisory opinion, if so requested, could perform at least three key functions.

First, the ICJ could clarify that P5s remain bound by peremptory norms and treaty obligations that limit their freedom to exercise the veto in atrocity contexts. Even a restrained opinion that affirms general principles would reinforce the view that veto use is not immune from law.

Second, the ICJ could elaborate on the scope of Article 27(3). Clear guidance on what constitutes a dispute, who is a party to it and when abstention is required would strengthen the argument that certain vetoes lack legal foundation. Although the Court cannot compel compliance, an authoritative interpretation would provide a basis for political challenge and potentially influence SC practice.

Third, the ICJ could address the concept of ultra vires vetoes. It is unlikely to declare that an improper veto is void in a manner that deems a blocked resolution adopted. Yet, it could state that the exercise of the veto in breach of fundamental norms is inconsistent with the Charter. Such a finding would inform the conduct of Member States outside SC, including the use of the Uniting for Peace procedure or collective action to uphold peremptory norms. Fourth, an advisory opinion would shape discourse. Even if ignored in the short term, advisory opinions influence how states articulate their positions over time, how civil society frames expectations, and how diplomats negotiate norms.

There are, of course, risks. The ICJ may craft an opinion so cautious that it adds little: In its 1971 Namibia advisory opinion, the ICJ itself cautioned that it is not an appellate body over the Council (para. 89). P5s may dismiss the opinion or portray it as an encroachment SC’s prerogatives. One 2001 study found that in six advisory opinions in which individual states were requested and expected to implement the Court’s findings, none did so, except those involved in the 1949 Reparation for Injuries advisory opinion.

The bottom line regarding the effectiveness of the advisory opinion lies in the framing of the resolution and the question posed to the ICJ. An effective request would avoid reference to specific conflicts, anchor the inquiry in Charter provisions that already command wide acceptance, and treat the prevention of atrocity crimes as the operative legal trigger. Rather than inviting the ICJ to pronounce on the legality of particular vetoes, the question should ask, in general terms, what obligations flow from the Charter and international law when voting rights are exercised in such situations, and the legal consequences for P5s and UN organs in the event of non-compliance.

The request for an advisory opinion on the P5 veto could be drafted in broad, yet concise, terms:

“What obligations do members of the Security Council, including the permanent members, have under the Charter of the United Nations and international law when exercising their voting rights under the Charter’s Article 27 in situations involving a serious risk of, or the commission of, genocide, crimes against humanity, or war crimes?

How should Article 27(3) of the Charter, requiring a party to a dispute to abstain from voting on decisions under Chapter VI and Article 52(3), be interpreted and applied in such situations?

Do obligations arising under international law, including peremptory norms, impose legal constraints on the exercise of voting rights under Article 27 where their use would impede action aimed at preventing or bringing to an end such crimes?

What legal consequences follow, within their respective competences, for the Member States concerned and for the organs of the United Nations, in particular the General Assembly, where those obligations are not complied with?”

Conclusion

The debate over the SC veto is unavoidable in a period marked by repeated failures of collective security. Attempts to reform the SC through a Charter amendment are unlikely to succeed. Instead, states have pursued procedural innovations and voluntary restraint initiatives that, while limited, signal an evolving normative environment. Alongside these developments, legal arguments that constrain veto use under peremptory norms and treaty obligations have become more prominent.

An ICJ advisory opinion would not transform SC practice overnight. Nor would it eliminate the structural asymmetries that shape the veto. Yet, the possibility that the Court might clarify the law should not be dismissed. An advisory opinion could consolidate emerging normative expectations, reinvigorate (neglected) Charter provisions, and reassert the role of legal principle in the governance of collective security. Even modest judicial guidance would meaningfully contribute to the gradual recalibration of how the veto is perceived and exercised.