Treaty Interpretation in the ICJ’s Opinion on the Right to Strike

On 21 May 2026, the International Court of Justice delivered its advisory opinion on the Right to Strike under ILO Convention No. 87. The question before the Court was whether the Freedom of Association and Protection of the Right to Organise Convention, 1948 (Convention No. 87) protects workers’ right to strike. The core of the case concerns a question of treaty interpretation: does Convention No. 87 protect the right to strike, despite containing no express reference to it? The political stakes behind the legal question are plain. The opinion arrives at a moment when right-wing governments have been seeking to erode labour protections, and when changes in the global economy have made the exercise of collective labour rights more difficult than ever — from the displacement pressures of automation to the disruptions posed by the gig economy, and the transformative rise of AI. A finding that the Convention does not protect the right to strike could have been a trigger for rolling back domestic labour protections, with rippling effects for other international instruments that incorporate labour standards by reference to Convention No. 87. By contrast, a positive finding enshrining the right to strike in this fundamental convention would provide important legal ballast for workers worldwide.

In its Advisory Opinion, the Court concluded that Convention No. 87 does indeed protect the right to strike. The Court confined itself to the question presented, engaging in a thorough and methodologically open exercise in treaty interpretation — on which we focus here. We note at the outset that the Court’s positive identification of the right to strike in Convention No. 87 marks, in our view, a weclome and significant step forward in the decade-long conflict among the Organisation’s tripartite constituents. However, the margin of the vote (10–4) risks obscuring some of the foundational disagreements that divided the Court. (Judge Okowa did not participate, having been a member of the ITUC’s legal team before being sworn in as a judge.)

Turning to the question of treaty interpretation: in our view, the Court chose an expansive path, making significant methodological innovations in the process. There were good reasons for the Court to proceed as it did: the conflict within the ILO had been long-standing, and there were incentives to provide the most robust answer possible, given the various constituencies involved. Yet the expansive approach invited four strong dissents, as well as seven declarations and separate opinions that engaged, with varying degrees of disagreement, the Court’s approach to treaty interpretation under the Vienna Convention on the Law of Treaties (VCLT).

The Advisory Opinion settles the dispute over the existence of the right to strike — the Court’s answer is clear, although battles over the scope of that right will continue. Yet the opinion opens new lines of inquiry into foundational questions of treaty interpretation. In what follows, we first set out the Court’s reasoning and what we see as the expansive scope of its interpretative approach. We then turn to two questions that the opinion opens in relation to Articles 31 and 32 of the VCLT: the role of subsequent practice and the scope of relevant (extrinsic) rules of international law.

I. The Court’s Expansive Case for the Right to Strike

The Court’s analysis begins with Article 31(1) of the VCLT. Its point of departure is that Convention No. 87 contains no explicit reference to the right to strike (¶67). Absence of an express provision does not, however, mean that such a right is excluded: rather, as the Court puts it, exclusion is ‘only warranted when the text of all the provisions concerned, their context and the object and purpose of the treaty point to it’ (¶68).

In the Court’s view, the key locus of an implicit right to strike is Article 3(1) of Convention No. 87:

Article 3(1): Workers’ and employers’ organisations shall have the right to draw up their constitutions and rules, to elect their representatives in full freedom, to organise their administration and activities and to formulate their programmes.

The ordinary meaning analysis hinges on the term ‘activities’. As the Court notes, Articles 2 and 10 grant workers and employers the right to form organisations for the purpose of furthering their respective interests; Article 3(1) guarantees those organisations the right to ‘organise their administration and activities’. Reading these provisions together, the Court finds that strike action falls within the ordinary meaning of ‘activities’: a strike — defined in the opinion as ‘an activity consisting of a temporary work stoppage or slowdown wilfully effected by one or more groups of workers with a view to enforcing or resisting demands or expressing or supporting grievances’ — is ‘capable of falling within’ that term (¶69–70).

In the Court’s view, the Convention’s object and purpose reinforce that reading: its aim is to ‘guarantee freedom of association as a means of improving labour conditions and achieving sustained progress’ (¶72), and strike action is one of the main tools used by workers and their organisations to promote their interests and improve conditions of labour (¶73). As Judge Cleveland vividly puts it, ‘[w]orkers do not form organizations to play cards’; rather, they associate to bolster their collective power and use strikes as tools to fight exploitation and defend human dignity in the workplace (decl.: Cleveland, ¶5). The Court thus concludes that, under Article 31(1) of the VCLT, Convention No. 87 protects the right to strike (¶74).

The Court then turns to the three elements that ‘shall be taken into account’ under Article 31(3). There being no express subsequent agreement among the parties about the existence of the right to strike under Convention No. 87, the Court focuses its analysis on subsequent practice under subparagraph (b) and interpretation in light of relevant extrinsic rules of international law under subparagraph (c), sometimes referred to as ‘systemic integration’. 

On subsequent practice, the Court notes that to qualify as an authentic means of interpretation within the terms of Article 31(3)(b) of the VCLT, such practice must establish ‘a common understanding of the parties regarding the meaning to be given to a treaty’ (¶77). Over the years, various ILO supervisory bodies advanced, in progressively clearer terms, their view that Convention No. 87 enshrines the right to strike. However, a number of State parties expressed their ‘clear opposition’ to that interpretation at various junctures. The Court therefore concludes that the subsequent practice cannot establish the agreement of the parties on this point (¶87). So far, the Court’s moves are uncontroversial — at least on the level of methodology.

The Court takes a more innovative and consequential step in its approach to systemic integration under Article 31(3)(c). The Court holds that ‘relevant rules applicable in the relations between the parties’ need not be binding on all parties to the treaty being interpreted; it suffices that a rule expresses their ‘common understanding’ of certain provisions of the treaty under interpretation (¶90). On this basis, the Court treats as relevant rules contained in the ICESCR and the ICCPR (as interpreted by the Human Rights Committee), concluding that those rules confirm the right to strike is encompassed in the freedom of association protection afforded by Convention No. 87 — despite the fact that a handful of parties to Convention No. 87 are not parties to either instrument. The Court considers this legitimate because the practices of those non-parties were broadly consistent with the position under the ICCPR and ICESCR on the right to strike (¶94), and because parties to the covenants had not made relevant reservations or raised significant objections to the right to strike thereunder (¶95) — both features assist in establishing a ‘common understanding’ under Article 31(3)(c) (¶96).

Having satisfied itself that Article 31 yields a clear and unambiguous answer (¶101), the Court nonetheless turns to Article 32 to confirm its view. It looks first to the travaux préparatoires. These yield an inconclusive result: ‘the intention of the drafters of Convention No. 87 with respect to the right to strike in general is unclear and the question was left open’ (¶111). 

More novel is the Court’s use of Article 32 to take a second look at subsequent practice. To qualify as an authentic means of interpretation under Article 31(3)(b), recall, subsequent practice must establish a ‘common understanding’ among the parties. Under Article 32, by contrast, subsequent practice functions as a supplementary means of interpretation and carries no such requirement (¶77). On this basis, the Court concludes that ‘the fact that a significant majority of States parties to Convention No. 87 considers that the Convention protects the right to strike, as reflected by the subsequent practice of those States parties, is an element that must be taken into account as a supplementary means of interpretation’ (¶115, emphasis added) — one that confirms its earlier finding under Article 31.

Finally, the Court gives ‘great weight’ to the interpretations advanced by the ILO’s supervisory bodies as further supplementary means of interpretation, and also considers as relevant the pronouncements of regional courts or bodies interpreting regional conventions. Both lines confirm that Convention No. 87 protects the right to strike.

II. Innovations and Controversies

A. Subsequent Practice: A Second Bite at the Apple

In what appears to be a first for the Court, the majority accepts that subsequent practice falling short of the Article 31(3)(b) threshold — that is, practice failing to establish a common understanding among all of the parties — may nonetheless be considered as a supplementary means of interpretation under Article 32. As a supplementary means, it carries a different weight from authentic practice under Article 31(3)(b), but it is given weight nonetheless. On this basis, the Court treats as confirmatory the fact that a ‘significant majority’ of Convention No. 87 parties considers the Convention to protect the right to strike (¶115).

Judge Tomka objects to what he sees as a second bite at the apple. The distinction that the Court draws is, in his view, based on a ‘misunderstanding’ of the work of the International Law Commission (diss.: Tomka, ¶33). In Judge Tomka’s view, ‘[f]or the purposes of treaty interpretation, an understanding that is not shared by all the parties is no understanding at all’ (diss.: Tomka, ¶34). The precise question of what the ILC had in mind is contested and need not be resolved here. What is clear is the practical consequence: inconsistent practice, held below the threshold of Article 31(3)(b), is admitted through the Article 32 door and assigned confirmatory weight. By giving interpretative heft to the practice of a ‘significant majority’ of parties, the Court’s approach opens the door to at least a degree of majoritarianism in interpretation — moving in the same direction as, if not going quite so far as, the notion of ‘European consensus’ deployed by the European Court of Human Rights.

B. Article 31(3)(c): Lowering the Bar for Systemic Integration?

The second node of methodological innovation concerns the threshold for systemic integration under Article 31(3)(c). As noted in Section I, the Court holds that the requirement that ‘relevant rules of international law’ be ‘applicable in the relations between the parties’ does not demand that all parties to the treaty under interpretation be bound by those rules. It suffices that the rule in question expresses a ‘common understanding’ among the parties regarding certain provisions of the treaty under interpretation. On this basis, the Court treats rules contained in the ICESCR and the ICCPR as relevant elements of interpretation, tending to establish that Convention No. 87 protects the right to strike. 

This standard for systemic integration draws criticism from several judges. Judge Hmoud sets a higher bar: for a rule to qualify under Article 31(3)(c), ‘it should be a rule of general international law that applies between all the parties to Convention No. 87’ (diss.: Hmoud, ¶29). Judge Tomka presses the point further: ‘[a] rule that does not bind all parties is an awkward vehicle for expressing what they are said to hold in common’ (diss.: Tomka, ¶66).

Other judges criticise the way in which the Court draws on rules from other treaties. Judge Abraham addresses the case of the four states that participated in the proceedings and were parties to both Convention No. 87 and the covenants, yet opposed the view that Convention No. 87 protects the right to strike. The Court relies on the absence of reservations to the Covenants by two of those states (Costa Rica and Switzerland) and on the fact that the reservation entered by the other two (Bangladesh and Japan) did not purport to exclude the right to strike. Judge Abraham is not persuaded. A state’s consent to an explicit obligation under the ICESCR is, in his view, ‘in no way contradictory’ with that state contesting the same obligation under another instrument that makes no mention of it (diss.: Abraham, ¶47). Judge Nolte, while agreeing that the rules applicable under Article 31(3)(c) need not formally bind all parties to Convention No. 87, disagrees with how the Court applies that standard to the four State parties to Convention No. 87 that are not parties to both Covenants. The case of Saint Lucia — for which the Court could identify no ‘positive indication’ of its position — illustrates the difficulty: here, in Judge Nolte’s view, the Court ‘goes too far in assuming consent’ (sep. op.: Nolte, ¶29). For Judge Nolte, ‘mere non-objection, toleration or acquiescence cannot, without more, establish a sufficient commonality for the purpose of identifying a consent-based, authentic element of treaty interpretation under Article 31’ (sep. op.: Nolte, ¶29).

Conclusion

Only four of the fourteen participating judges dissented; 10–4 represents a strong majority in favour of finding the right to strike protected under Convention No. 87. But the vote tally masks deeper unease about foundational methodological questions. The Court takes clear and innovative stances that point toward an expansive judicial role in interpretation — one less explicitly tethered to State consent. Most significantly, it endorses giving interpretive weight to non-universal state practice (albeit only as a supplementary means) and lowers the bar for systemic integration. Several judges supported this approach, while some would have preferred the Court to reach its result through evolutive interpretation (sep. op.: Gómez Robledo) or more minimalist reasoning (sep. op.: Nolte). Disagreements, in turn, were formulated in strong terms. Judge Tomka does not mince words: ‘[i]n its search for an interpretive leprechaun, the Court approaches the requirement of State consent not as the foundation of treaty interpretation, but as a residual obstacle to be overcome’ (diss.: Tomka, ¶83). Judge Xue is equally direct: ‘[t]he majority’s response to the request […] largely reflects an exercise of human rights advocacy rather than treaty interpretation’ (diss.: Xue, ¶3). 

Given the agreement on the result, one wonders why the majority chose an expansive approach. A more minimalist posture might have sufficed, avoiding the tension between keeping treaties relevant through ex post judicial interpretation and adhering to the bargain struck ex ante. 

Ultimately, however, the Court did something valuable in laying out its methodology in such transparent terms, a step too often avoided by other international courts and tribunals. In doing so, it necessarily subjected itself to significant methodological criticism. And this is positive in and of itself. In our view, Judge Nolte captured the spirit of judicial treaty interpretation well: rules of interpretation ‘formulate the expectation that interpreters articulate their reasoning in terms of certain generally recognized criteria’ and ‘serve to make the interpretative process, including deliberations among different interpreters, reach an appropriate level of complexity and transparency’ (sep. op.: Nolte, ¶61). This opinion is a case in point: the candour of the Court’s interpretative approach is precisely what enables assessment and criticism by the legal community.