Iran’s “new rules”: legal under UNCLOS or not? Hormuz tensions rise as Trump backs a US blockade

Iran on Saturday said it will enforce “new rules” over waters along its coastline in the Arabian Sea and the Strait of Hormuz, describing the waters as a source of “security and prosperity for the region."

The announcement came as US Treasury Secretary Scott Bessent reaffirmed that the US naval blockade of Iranian ports would remain in place until freedom of navigation in the waterway returns to “pre-February 27” levels.

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Iran draws the line

The Islamic Revolutionary Guard Corps (IRGC) Navy said it would exercise “control over nearly 2,000km of Iran’s coastline” and turn the waters into “a source of pride and power for the dear people of Iran,” per Al Jazeera.

Iran had earlier offered to reopen the Strait of Hormuz, the chokepoint that handles a fifth of global energy trade, if Washington lifted its blockade, while also suggesting that nuclear talks be deferred to a later phase.

Washington rejected that proposal.

UNCLOS says no blocking—so where does Iran’s Hormuz play stand?

Under international maritime law, the Strait of Hormuz is not simply open water. It is a legally protected corridor. The United Nations Convention on the Law of the Sea, known as UNCLOS, establishes what is called a "transit passage" regime for straits used in international navigation.

In plain terms, this means ships and aircraft have an explicit right to pass through, that right cannot be blocked or suspended, and the states bordering such straits are legally prohibited from standing in the way.

Coastal nations do retain some authority. They can set rules around maritime safety, pollution control, and traffic management. But crucially, those rules cannot be used as a backdoor to choke off passage in practice.

The Strait of Hormuz, through which roughly a fifth of the world's oil flows, is precisely the kind of waterway UNCLOS was designed to keep open.

There is, however, a significant legal wrinkle. Iran signed UNCLOS on the day it opened for signatures. December 10, 1982, but UN Treaty Collection records indicate it has never formally deposited its ratification. That distinction matters more than it might appear. Ratification is what makes a treaty binding.

This means UNCLOS does not bind Iran with the same legal force it carries for the more than 160 states that have fully ratified it.

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Pay up or reroute

Any ships transiting the Strait are being targeted by IRGC fast attack boats, forcing them to move through Iran’s territorial waters and pay tolls.

A Lloyd’s List report last month said vessels were navigating around Iran’s Larak Island and that countries were paying as much as $2 million per ship to pass through safely.

Tehran has also sought US recognition of Iran’s sovereignty over the strait and proposed splitting tolls with Oman.

Tensions spike oil prices

The US response has been equally hardline.

While announcing the blockade in April, President Donald Trump said the Navy would “interdict every vessel” paying “an illegal toll,” and he also issued a “shoot and kill” order against small Iranian boats that deploy mines to choke traffic through the strait.

Crude prices have risen sharply amid the disruption, with Brent briefly topping $122 a barrel and earlier crossing $125.