By Priya Raman

The International Court of Justice has held, in an advisory opinion of 21 May 2026, that the right to strike of workers and their organizations is protected under ILO Convention No. 87 of 1948. The Court answered a question referred by the ILO Governing Body: "is the right to strike of workers and their organizations protected under the Convention (No. 87)?" The dispute originated within the ILO, where the Employers Group contested that the freedom of association convention covered strikes at all.

Convention No. 87 contains no explicit reference to the right to strike. The Court adopted a functional and teleological approach, reading the treaty's terms in good faith, in context, and in light of its object and purpose.

What does the ruling change?

The operative reasoning turns on Article 31(3)(c) of the Vienna Convention on the Law of Treaties, which requires that "any relevant rules of international law applicable in relations between the parties shall be taken into account when interpreting a treaty." The Court treated this as a mandate, not an option. Yet the provision affords the interpreter flexibility in how an external rule informs the reading.

The central question was whether the ICESCR and the ICCPR, which protect the right to strike directly or through interpretive practice, could qualify as relevant rules despite the absence of an identity of parties. The Court held that a rule may be generally applicable if it expresses the parties' "common understanding" of the treaty under interpretation. President Iwasawa's separate opinion stressed that Article 31(3)(c) requires common understanding, not agreement, so not every party to Convention No. 87 must be bound by the external treaty.

The numbers did the work. Of the States parties to Convention No. 87, only 8 are not parties to the ICESCR, which has 173 States parties. Only 7 are not parties to the ICCPR, which has 175. Just four States party to Convention No. 87 belong to neither covenant. "In these circumstances, the Court considers that the two Covenants contain relevant rules that must be taken into account when interpreting Convention No. 87."

On the merits, the Court found that "strike action is one of the main activities engaged in and tools used by workers and their organizations to promote their interests and improve conditions of labour thereby ensuring the effective exercise of the freedom of association protected under Convention No. 87." Denying the right to strike would, in effect, defeat the treaty's object and purpose.

What are the practical consequences for practitioners?

For governments and employers, the opinion forecloses the argument that Convention No. 87 is silent, and therefore neutral, on strikes. For unions and their counsel, it supplies an ICJ-endorsed textual basis to challenge strike bans or restrictive domestic regulation as violations of freedom of association. Treaty litigators should note the method: systemic integration now operates on a "high degree of overlap" in membership rather than strict identity of parties. That standard invites future arguments over how much overlap suffices. The caveat is real; the Court did not define the threshold.

What did the judges not say?

Judge Nolte, while agreeing that external rules need not formally bind all parties, cautioned against diluting the principle of consent underpinning Article 31(3)(c). Judge Bhandari's separate opinion similarly insisted that systemic integration be applied cautiously and consistently with state consent. Judge Xue dissented on the premise that all three instruments are human rights treaties of the relevant kind.

A recent commentary by Siobhán McInerney-Lankford, a human rights lawyer at the EU Fundamental Rights Agency writing in a personal capacity, endorses the Court's approach while flagging its open questions. How is a rule distilled from the external treaty's provision? What constitutes a "high degree of overlap," and by what indicators? What evidences a "common understanding"? The opinion promises coherence. It does not yet deliver a method.

The commentary also notes a structural point. Human rights treaties generate both horizontal accountability between states and vertical accountability toward rightsholders, which makes an identity-of-parties requirement virtually impossible to satisfy in this field. Even so, the author warns that "common understanding" must not stretch so far beyond identity of parties as to vitiate consent entirely. That balance, not the headline holding, will define the opinion's long-term reach.

The opinion arrives amid direct challenges to multilateralism and regional human rights systems. An interpretative approach favoring alignment and coherence is, on that view, welcome. Whether lower-cost coherence comes at the price of consent remains the unanswered question.

In plain words: the ICJ says Convention 87 protects the right to strike, and it reached that result by counting treaty memberships rather than requiring all parties to match.