Subsidiary means for the determination of rules of international law

On 21 May 2026, the International Court of Justice delivered its advisory opinion on the right to strike under ILO Convention No. 87, holding by ten votes to four that the right is protected by that instrument. The Opinion clarifies a long-running issue between workers’ and employers’ groups. But it is also significant as a methodological case. The Court majority concludes that the ordinary meaning of the terms of the treaty, read in good faith, in the context, and in light of the object and purpose of the treaty indicates that ILO Convention No. 87’s freedom of association provision encompasses the right to strike. Participants throughout the proceedings cited various other material to support their competing claims, including a variety of ILO treaty body output, which is in focus here. In responding to these claims, the Court majority constructs a framework for situating pronouncements of the ILO treaty supervisory bodies in the landscape of Article 31(3) and Article 32 of the Vienna Convention on the Law of Treaties. The Court’s approach will likely…