Fenella Billing is an Associate Professor at the Department of Law, Aalborg University, Denmark, where she teaches and researches in areas related to human rights and international law, EU law and comparative law.

The Hormuz Strait is still a contentious chokepoint in international shipping. On 13 July 2024, the US President, Donald Trump, posted on social media that the conflict with Iran was reigniting, and that at the same time he was intending to charge a 20% fee on passing cargo, for safe convoy by US vessels through the straight, though not in relation to Iranian flagged vessels, ships coming to and going from Iranian ports, and ships carrying Iranian cargo, which would be subject to the so-called ‘Iranian Blockade’. Within 24 hours, the President himself pulled back the idea of the toll (and replaced it with a scheme he claimed would involve immense investment in the US by the Gulf states), while maintaining that the Iranian Blockade was in place.  The blockade (again) raises a myriad of questions. However, this post is experimental and evaluates the legality and enforceability of the proposed fee.

Transit passage and innocent passage under UNCLOS

In times of peace, there are two regimes contained in the United Nations Convention on the Law of the Sea (UNCLOS) that regulate the passage of vessels through international straits, such as the Hormuz Strait: transit passage and innocent passage. Firstly, all ships and aircraft enjoy the right of transit passage through international straits under the regime provided for in UNCLOS Articles 37-44. Even though the Persian Gulf is a semi-enclosed sea, much of the Gulf is regarded as the exclusive economic zone (EEZ) of the coastal states. The Hormuz Strait connects the Gulf to an EEZ or the high seas in the Gulf of Oman (leading into the Arabian Sea and then the Indian Ocean). The right of transit passage guarantees freedom of navigation and overflight “for the purpose of continuous and expeditious transit of the strait…” and for entering the territorial sea of one of the Gulf’s coastal states. Article 42(1)(a) allows bordering states to make rules for the safety of navigation of an international strait but does not expressly arm non-bordering states, such as the US, with the same power.

In addition, the right of innocent passage, which is regulated in UNCLOS Articles 17 to 26, applies in straits used for international navigation, such as the Hormuz Strait, under article 45(1)(b). This right shall not be suspended, according to Article 45(2). Under Article 21, the coastal state may adopt laws in conformity with international law for the safety of navigation. However, this provision does not expressly apply to states other than the relevant coastal states.

Article 26(2) provides that charges may only be levied by coastal states against foreign vessels innocently passing through the territorial sea for specific services rendered to the vessel (but they must be levied without discrimination, which would include Iranian flagged vessels, or vessels carrying Iranian cargo). Article 26 impliedly only applies to relevant coastal states and not other states. In other words, UNCLOS does not provide the US or any other state that is not a coastal state in the Persian Gulf with the authority to apply any fees or charges. Furthermore, the provision only applies to fees for specific services rendered and not to general tolls on passing ships. President Trump appeared to be proposing a fee of a general nature to ‘all passing cargo’ for the services rendered of providing for safety and security in the Strait. Furthermore, there is no express governance in the UNCLOS about the consequences of a failure to pay, and it seems difficult to comprehend how the system proposed by Trump would have been enforced.

In summary, applying the above rules in UNCLOS to the social media post by President Trump leads to a conclusion that President Trump’s proposed 20% fee for acting as the so-called ‘Guardian of the Hormuz Strait’ was arbitrary and would have been unlawful in its impediment to transit passage and innocent passage, potentially too general in its application, as well as discriminatory against Iran (in a peace-time framework). Not only that but its enforceability was highly questionable.

International customary law

The US and Iran are not parties to the UNCLOS, and thus the application of the provisions of UNCLOS to the actions of these two states in the current situation in the Hormuz Strait is uncertain. Nevertheless, the International Court of Justice (ICJ) in the Corfu Channel Case (ICJ Reports 1949, p. 28), a case which also dealt with transit passage through an international strait that joined EEZ areas or high seas on both sides, found that the right of innocent passage by foreign vessels in peacetime, including warships, is a part of customary law. Coastal states are thus required to ensure the safety of ships that are exercising the right of innocent passage through an international strait. This decision can apply in the Hormuz Strait in times of peace. The judgment applies the obligation to protect the safety of navigation to the Strait’s coastal states, who are in a strengthened legal position in relation to regulating a strait (such as Iran in the Hormuz Strait). Even though the US is not a coastal state and does not have the same legal obligation to provide for the safety of foreign vessels, charging a fee to guarantee the safe passage of a vessel that in any event has a right to innocent passage seems inconsistent with the object and purpose of the provision. However, privatization means that a state can be the provider of private services, yet logically not by force. This would be tantamount to an illegal capture.

In summary, the application of the transit passage and innocent passage regimes to the proposed US fee on all passing cargo was legally dubious at best and was generally incongruous with international law.

The situation of an armed conflict at sea

Putting the above aside, President Trump maintains that the armed conflict between the US and Iran has recommenced and thus the current situation needs to be assessed under the law of naval warfare.

Attacks against merchant vessels by Iran can be analysed under the law of targeting. For example, the Basic Rules in paragraphs 38-45 of the San Remo Manual on International Law Applicable to Armed Conflicts at Sea (San Remo Manual, 12 June 1994) limit the methods and means of warfare to military objectives, prohibiting attacks on neutral merchant vessels and limiting attacks on military targets according to the rules of proportionality. This also applies to overflight situations. Yet, The San Remo Manual does not provide conclusive answers to questions about the legality of President Trump’s proposed fee with the US as ‘Guardian of the Hormuz Strait’. For example, para 120 preempts safety convoys of neutral merchant vessels by accompanying neutral state vessels but not by belligerent states.

Conclusion

Even during armed conflict, the UNCLOS legal framework, which allocates state powers and duties in peacetime in the various maritime zones, generally applies. The UNCLOS provisions on transit passage and innocent passage did not provide the US with the authority to apply a 20% safe convoy fee to merchant shipping. Neither did the application of the right of innocent passage in international customary law, in line with the ICJ’s judgment in the Corfu Channel Case. In the context of President Trump’s statement, the Iranian Blockade can be tantamount to an illegal blockade. Of significance to this blog and the purported application of the 20% fee to all passing cargo, it is wholly unclear how the US could have made states accept the 20% fee, or what the consequences could have been if neutral vessels had refused to comply. It is difficult to imagine how the US could even guarantee safety of navigation in the Strait to the extent required to justify applying the fee. It is untenable that the innocent passage of neutral merchant vessels, or an accompanying neutral state convoy, can be stopped by forcibly requiring ships to accept a fee levied by the US, or that using force in these circumstances could ever be justified as an act of self-defence under Article 51 of the UN Charter.

Perhaps the most important point is that vessels should exercise caution about accepting the protection of the US (a belligerent) in the Hormuz Strait and into the Persian Gulf, lest they be (wrongfully or otherwise) regarded as military objectives.

Photo credit: Michael Afonso on Unsplash