Three Legal Constraints on U.S. Unilateral Deep-Sea Mining: The ISA’s Objective International Personality and Obligations of Cooperation and Due Regard (Part I) – Problems with the Customary Status of the Common Management Element

[Dr Ekaterina Antsygina is a Marie Skłodowska-Curie Postdoctoral Fellow at the Norwegian Centre for the Law of the Sea at UiT The Arctic University of Norway, working on the deep-sea mining on the Norwegian continental shelf.]

In 2025, the U.S. President Donal Trump issued an Executive Order promoting unilateral licensing for deep-sea mining not only on the U.S. continental shelf but also beyond national jurisdiction, in the international seabed (the “Area”). The Order relies on domestic legislation, the 1980 Deep Seabed Hard Mineral Resources Act (DSHMRA), which predates the adoption of UNCLOS. DSHMRA established an interim domestic legal regime for deep seabed mining (DSM) pending creation of the international regime of the Area. The 2025 Order attempts to revive this unilateral approach, asserting domestic regulatory competence over activities in the Area outside the framework of the International Seabed Authority (ISA). This development raises significant concerns that the application of domestic regulatory frameworks to activities in the Area risks fragmenting its legal regime, weakening environmental standards, and creating regulatory incoherence in a domain intended to be governed collectively.

In response, 39 Member States, together with the African Group (representing 49 countries) reaffirmed that the ISA is the sole internationally recognized institution with jurisdiction over the Area and its resources (FAQ 3). The ISA Council has likewise reaffirmed that the principle of the common heritage of humankind (CHH) constitutes a rule of customary international law binding on non-parties and may even qualify as a jus cogens norm (para 36). Counterarguments to this position rely on the freedom of the high seas and the persistent objector doctrine (Kraska, p. 504; Lodge, p.2), which could be invoked to contest the universality of Part XI obligations vis-à-vis non-parties.

While the present author agrees that the core elements of the CHH principle, such as benefit-sharing, marine environmental protection, reservation for peaceful purposes, and non-appropriation have crystallized into customary rules (see Lathrop,  Jaeckel, 2020, p. 663, Dingwall pp. 104-109), and that the U.S. cannot credibly invoke a persistent objector status with respect to these elements, the customary status of the common management of the resources exclusively through ISA (Articles 137(2) and 153(1) of UNCLOS) remains considerably more controversial. This controversy stems from the institutional limitations inherent in the ISA’s character as a treaty-based organ whose membership is confined to States Parties to UNCLOS.

At first glance, the conventional criteria for the customary law formation appear satisfied: under Article 38 (1) of the Statute of the International Court of Justice (ICJ), the existence of a customary rule requires sufficiently widespread, consistent, and representative general practice (Conclusion 8(1), p. 100) accompanied by opinio juris. Acceptance of the ISA’s central regulatory role is both widespread and representative: the ISA currently counts the majority of States as members, States made numerous statements in regard to the ISA’s exclusive mandate (para 36), and numerous States Parties have implemented Part XI through domestic legislation recognizing in various ways that activities in the Area may only be conducted with the involvement of the ISA (paras. 32, 35, 40, 42, 43, 49, 50, 54, 55, 90). Such practice appears consistent and normatively motivated. General practice need not be universal (Section 14(i), and a State may be bound even if it did not participate actively in the practice (Section 14(ii). From this perspective, the requirements for the crystallization of a customary rule establishing collective management exclusively through ISA could be considered fulfilled.

However, the assessment of general practice is not “simply a question of how many States participate in the practice, but which States” (Section 14, p. 26). As the ICJ emphasized in the North Sea Continental Shelf cases, the participation of the “specially affected” States is of particular importance (para. 74). The U.S. is undoubtedly a “specially affected” State in the context of DSM due to its involvement in UNCLOS III and 1994 Agreement negotiations, numerous attempts to ratify UNCLOS, its domestic legislation on DSM and technological capacity. 

It is precisely U.S. practice that reveals a structural difficulty in the customary law formation in respect to common management through the ISA: the U.S. cannot engage in the ISA’s practice equivalently to the ISA members States (and it cannot become one without ratifying UNCLOS). Although the U.S. has participated in the ISA meetings as a provisional member for four initial years and as an observer since 1998 until 2024, such participation is not functionally equivalent to membership. Only members may sponsor contractors, vote at the Assembly and Council, or participate fully in the adoption of the Mining Code.

This raises a deeper doctrinal question: can a customary rule crystallize around the exclusive authority of a treaty-based institution when non-parties are structurally prevented from engaging in equivalent practice? Classical custom presupposes that all States are at least formally capable in engaging in conforming or contrary conduct. Treaty-based institutional regimes may differ in this respect: by virtue of non-participation, a State may be barred from engaging in the very conduct that would shape general practice.

The equivalence of practice has not been explicitly discussed by international tribunals, ILC or ILA as an element of the customary law formation. In its recent Advisory Opinion on climate change, the ICJ referred to the possibility of “equivalent practice” in the fulfilment of customary obligations relating to climate change (para. 315). This reasoning implies that all States should, at least in principle, be capable of engaging in comparable forms of practice relevant to the development and implementation of customary rules. However, the exceptional and institutionally limited nature of certain treaty-based bodies may prevent such equivalence of practice. Where participation in a specific institutional mechanism is limited to treaty parties, non-parties are structurally unable to engage in the same forms of conduct, particularly where comparable conduct outside the institutional framework would be considered unlawful.

In these circumstances, if a State cannot engage in the relevant practice on the same footing as members of an institution, its abstention from such practice cannot automatically be interpreted as acquiescence in the institution’s exclusivity. The absence of equivalent practice therefore complicates the inference not only of the general practice but also opinio juris and challenges the assumption that collective management exclusively through the ISA has attained customary status binding on non-parties. More fundamentally, the lack of functional equivalence calls into question whether practice within such institutions can contribute to the formation of customary rules binding on non-parties at all.

This is important to distinguish: the practice of treaty-based organs, as well as that of States-members acting within such organs, may contribute to the formation of customary international law (Conclusion 4(2)).  However, a treaty-based rule that confers exclusive competence on such organs and renders the activities of non-members illegal cannot, as such, crystallize into customary law. Accepting the contrary would effectively exclude non-parties from engaging in activities that would otherwise remain open to all States. This, in turn, would undermine the possibility of generating the practice of “specially affected” States required for the formation of customary law.

An analogy may be drawn with institutions such as the Commission on the Limits of the Continental Shelf (CLCS), or treaty-based dispute-settlement mechanisms. Engagement by non-parties with such bodies would not trigger the formation of customary rules establishing the exclusivity of such institutions vis-à-vis non-parties. For instance, although the CLCS has received 98 submissions from Party States concerning the outer limits of extended continental shelves (ECS), and non-parties has engaged in communications with the CLCS, it is not a customary rule that making such a submission is a legal obligation for all States (part 8 of Article 76 refers to coastal States, not States Parties), or that it is necessary for enjoying sovereign rights over the ECS or for the recognition of such outer limits (p. 391), or that coastal States cannot establish outer limits without using the mechanism of the CLCS.

Similarly, the compulsory character of the dispute-settlement mechanism established under UNCLOS cannot crystallize into customary law merely through widespread use by States Parties (and even endorsements of the decisions by non-parties), since this would run counter to the pacta tertiis rule (VCLT, Article 34) and the principle of state sovereignty.

This institutional asymmetry renders the customary status of exclusive common management far less straightforward than is often assumed. Within the DSM regime, such rules as exclusive alienation through the ISA, or dispute settlement through the Seabed Disputes Chamber, are unlikely to crystallize into customary international law capable of binding third States. 

At the same time, the Area forms part of the global commons, and its governance is intended to be centralized and to serve the benefit of humanity as a whole. Even if the ISA does not enjoy exclusive authority over all DSM activities as a matter of customary international law, this does not necessarily imply that unilateral action by non-parties is consistent with international law. As Waldock observed, it is a fundamental principle that a State cannot claim the benefits of a legal regime while disclaiming the obligations attached to it; in particular, a State making use of a regulated international space must comply with the rules governing such use (p. 28). Therefore, Part II of this blogpost analyzes limitations to the U.S. unilateral activities in the Area.