Francesca Marinelli (Università degli Studi di Milano)

1. The Dispute Behind the Advisory Opinion

On 21 May 2026, the ICJ delivered its long-awaited Advisory Opinion on the Right to Strike under ILO Convention No. 87, following a request made pursuant to Article 37 of the ILO Constitution.

The Advisory Opinion is noteworthy, first, because the proceedings themselves were exceptional from a procedural standpoint: prior to the present request, the advisory mechanism under Article 37 had been invoked for this purpose only once, in 1932, when the Permanent Court of International Justice was asked to interpret the Convention concerning Night Work of Women (see Boisson de Chazournes,  p. 197).

Secondly, the Advisory Opinion is notable because, although the present proceedings were prompted by a single question –  whether Convention No. 87 protects the right to strike (see the ILO Governing Body’s Request, 10 November 2023) –  that question had divided governments, employers and workers within the ILO for decades. This was due to the fact that Convention No. 87 contains no explicit reference to the right to strike. Nevertheless, since the 1950s, the ILO’s supervisory bodies – most notably the Committee on Freedom of Association (CFA) and the Committee of Experts on the Application of Conventions and Recommendations (CEACR) – have progressively developed the view that the right to strike is an essential corollary of freedom of association. This interpretation did not, however, remain uncontested. Since the late 1980s, and with increasing intensity after the end of the Cold War, the Employers’ Group has argued that neither the text nor the preparatory work of Convention No. 87 supports such a right (see Seifert, p. 487 and Vogt, Bellace et al).

Over time, the dispute extended well beyond the interpretation of Convention No. 87, coming to question the authority of the ILO supervisory bodies themselves and ultimately culminating in the institutional crisis that paralysed the Organisation’s supervisory machinery in 2012 (Maupain, p. 123). Although that crisis was eventually resolved, the underlying disagreement remained (on that point see Bellace).

Against this background, the Governing Body decided in 2023 – by a relatively narrow majority of 33 votes out of 56 – to request an advisory opinion from the ICJ in the hope of restoring legal certainty.

The Court answered the question referred to it in the affirmative by ten votes to four. The lack of unanimity is revealing. As the separate and dissenting opinions make clear, the issues before the Court admitted competing interpretations of Convention No. 87. The Advisory Opinion is therefore significant not only for the conclusion it reaches, but also for the interpretative reasoning on which that conclusion rests.

The Court’s reasoning is all the more significant because, although the Court formally confined itself to the question referred by the Governing Body, it addressed a number of broader issues that had arisen during the proceedings. In explaining why the right to strike falls within the scope of Convention No. 87, the Court clarified the methodology governing the interpretation of ILO conventions under general international law, provided important guidance on the place of the ILO supervisory bodies in that interpretative framework and on the notion of strike action, and situated the freedom of association guaranteed by Convention No. 87 within the broader framework of international human rights law.

Taken together, these features make the Advisory Opinion worthy of closer examination.

2. Reading the Right to Strike into Convention No. 87

In determining whether Convention No. 87 protects the right to strike, the ICJ applied the interpretative framework set out in Articles 31 and 32 of the Vienna Convention on the Law of Treaties (VCLT), which it regarded as reflecting customary international law notwithstanding that Convention No. 87 predates the VCLT.

Applying Articles 31(1) and (2), the Court interpreted the Convention in accordance with its terms, read in context and in light of the treaty’s object and purpose.

Although Convention No. 87 contains no explicit reference to the right to strike, the Court rejected the argument that such silence necessarily implies exclusion. Instead, it asked whether the right could be derived from the Convention’s text, structure and purpose. Focusing on Articles 2, 3 and 10, which safeguard workers’ organisations and define them as bodies established to promote and defend workers’ interests, the Court concluded that the Convention protects not only the existence of trade unions but also their ability to pursue those objectives effectively.

Central to the Court’s reasoning was the broad notion of “activities” in Article 3(1). In interpreting that provision, the Court relied on the CFA’s definition of a strike as “an activity consisting of a temporary work stoppage or slowdown willfully effected by one or more groups of workers with a view to enforcing or resisting demands or expressing or supporting grievances” (see the text here, p. 148, para. 783).  On that basis, it concluded that strike action constitutes one of the “activities” protected by Article 3(1) and therefore falls within the scope of Convention No. 87.

The Court further held that the right to strike derives from the functions of workers’ organisations and is confirmed by the Convention’s structure, object and purpose. While Articles 8 and 9 provide for specific limitations, the Convention contains no provision excluding strikes, and its preamble links freedom of association to improved working conditions and social progress, objectives for which strike action has traditionally been a principal means.

Having reached that conclusion under Article 31(1) and (2), the Court turned to Article 31(3) VCLT. It first considered whether the long-standing interpretation adopted by the ILO supervisory bodies could be regarded as subsequent agreement or subsequent practice. Finding no subsequent agreement under Article 31(3)(a), the Court held that the jurisprudence of the CEACR and the CFA does not constitute subsequent practice within the meaning of Article 31(3)(b). Although those bodies enjoy considerable interpretative authority, their pronouncements are neither acts of States nor evidence of an agreement between States parties concerning the interpretation of the Convention. The persistent opposition expressed by a number of States and, in particular, by the Employers’ Group prevented the emergence of the common understanding required by Article 31(3)(b).

The Court instead relied on Article 31(3)(c), clarifying that the “relevant rules of international law” referred to in that provision need not be binding upon every party to the treaty under interpretation. The Court relied in particular on Article 8(1)(d) of  the International Covenant on Economic, Social and Cultural Rights (ICESCR), which expressly recognises the right to strike, and to Article 22 of the International Covenant on Civil and Political Rights (ICCPR), which has been consistently interpreted by the Human Rights Committee as encompassing strike action within the protection afforded to freedom of association. Given the substantial overlap between the States parties to Convention No. 87 and the parties to the two Covenants, the Court considered these instruments part of the broader normative context relevant to the interpretation of the Convention.

Finally, the Court examined the supplementary means of interpretation under Article 32 VCLT. It adopted a broad understanding of that provision, taking into account not only the preparatory work and the circumstances surrounding the Convention’s adoption, but also the practice of the ILO supervisory bodies, subsequent State practice falling short of Article 31(3)(b), and the jurisprudence of regional human rights systems. Although the preparatory work was ultimately inconclusive, the Court attached great weight to the long-standing and influential interpretation developed by the CEACR and the CFA. Read together with subsequent State practice and the converging approaches adopted within regional human rights law, those materials confirmed the interpretation reached under Article 31.

3. The Broader Significance of the Advisory Opinion

As noted above, the significance of the Advisory Opinion extends beyond the recognition of a right to strike under Convention No. 87. Although the Court formally answered only the question referred by the ILO Governing Body, its reasoning speaks to a number of issues of broader relevance. It sheds light on the relationship between international labour law and international human rights law, the interpretation of ILO Conventions under general international law, the role of the ILO supervisory bodies in that interpretative exercise, and the scope of the notion of strike action itself.

First, the Court adopts a functional understanding of the right to strike. It recognises strike action not as an end in itself, but as an essential guarantee of trade union freedom, itself a specific manifestation of the broader right to freedom of association. In doing so, the Court reinforces the human rights dimension of Convention No. 87, confirming that it cannot be interpreted in isolation from the broader framework of international human rights law.

At the universal level, the Committee on Economic, Social and Cultural Rights has progressively developed its interpretation of labour rights under the ICESCR, emphasising in General Comment No. 23 (2016) that the right to strike constitutes a crucial means of introducing, maintaining and defending just and favourable conditions of work. Likewise, although the ICCPR contains no express reference to the right to strike, the Human Rights Committee has progressively interpreted Article 22 as encompassing strike action within the protection afforded to freedom of association. This converging understanding found its clearest expression in the Joint Statement adopted by the Committee on Economic, Social and Cultural Rights and the Human Rights Committee in 2019, in which the Committees recalled that the right to strike is the corollary to the effective exercise of the freedom to form and join trade unions (Committee on Economic, Social and Cultural Rights and Human Rights Committee, Statement on freedom of association, including the right to form and join trade unions, para. 4).

A similar trend has emerged across the regional human rights systems, which, despite their different institutional designs and legal bases, have progressively converged on a common functional understanding of the right to strike. The European Committee of Social Rights has long interpreted Article 6(4) of the European Social Charter, progressively clarifying the scope of the right to strike and the permissible limitations on its exercise. Likewise, the European Court of Human Rights has progressively interpreted Article 11 ECHR in the light of international labour law and other relevant international instruments (see Demir and Baykara v. Turkey, Enerji Yapı-Yol Sen v. Turkey and Humpert and Others v. Germany). Similarly, the Inter-American Court of Human Rights has interpreted the American Convention and related inter-American instruments as recognising the right to strike as a fundamental component of freedom of association and trade union rights (Advisory Opinion OC-27/21). In the Advisory Opinion at issue, the Court further observed that similar approaches have also emerged within the African and Arab regional human rights systems. This convergence across different regional frameworks reinforces the conclusion that the relationship between freedom of association, trade union rights and strike action has gained recognition beyond the institutional framework of the ILO.

Secondly, the Court treated Convention No. 87 like any other international treaty, applying the ordinary rules of treaty interpretation reflected in the Vienna Convention. This was by no means self-evident. Several participants had argued that the ICJ should attach particular weight to the intentions of the ILO’s tripartite constituents, reflected in the Convention’s preparatory work, given the distinctive institutional character of the Organisation and the unique process through which ILO conventions are negotiated and adopted. The Court rejected that approach. While acknowledging the institutional specificity of the ILO, it confirmed that its conventions remain subject to the general law of treaties and must therefore be interpreted in accordance with the customary rules reflected in the Vienna Convention.

Thirdly, the Opinion provides guidance on the legal status of the ILO supervisory bodies. While rejecting the argument that the jurisprudence of the CEACR and the CFA constitutes subsequent practice attributable to States under Article 31(3)(b) VCLT, it nevertheless attached “great weight” to their interpretations as supplementary means of interpretation under Article 32. In doing so, the Court charted a middle course. It neither recognised the supervisory bodies as authentic interpreters of Convention No. 87 nor reduced their jurisprudence to a merely persuasive source of guidance. Rather, it acknowledged their distinctive institutional authority, while preserving the distinction between expert supervision and treaty interpretation under the law of treaties.

Finally, although the Court formally limited its analysis to the question submitted by the ILO Governing Body, the significance of the Opinion arguably extends much further. By embracing a broad understanding of the right to strike, it may have influenced the very boundaries of the collective action protected under Convention No. 87. This is especially important because the contemporary debate has shifted from whether the right to strike exists to how far the protection afforded by Convention No. 87 extends to the various forms of collective action. This may prove particularly relevant for questions concerning sympathy strikes, secondary action, political strikes or other non-traditional forms of industrial action.

That said, before celebrating the Opinion as the definitive resolution of a controversy that has divided the ILO for decades, at least two important questions deserve closer attention.

The first concerns the legal effects of the Opinion itself. Although the ICJ has authoritatively clarified the meaning of Convention No. 87, the legal force of an advisory opinion delivered under Article 37 of the ILO Constitution remains uncertain.

The second concerns its institutional impact. Whether the Opinion succeeds in restoring consensus within the ILO remains to be seen.

What is already clear, however, is that its significance extends beyond the controversy that gave rise to it. Regardless of its practical effects within the Organisation, the Advisory Opinion is likely to be remembered not only for confirming that Convention No. 87 protects the right to strike, but also for reaffirming that international labour law forms part of the broader international legal order and must be interpreted in accordance with the general rules of international law, including international human rights law.