The United States could lawfully impose a blockade on the Strait of Hormuz even though the United Nations Convention on the Law of the Sea calls for uninterrupted transit, provided the operation follows the rules set out in the San Remo Manual, maritime attorney Adv. Yoav Harris told The Jerusalem Post.

Those rules require that both warring parties and neutral countries receive clear notice, that the blockade actually prevents passage, that enforcement applies equally to ships of every flag, that the measure is not aimed solely at starving civilians, and that humanitarian supplies reach the population when local stocks run short.

Washington announced its blockade after Tehran declared its own closure of the strait on March 4, 2026, days after joint US and Israeli strikes on Iranian targets began.

Despite the parallel announcements, the two actions receive different treatment under international law.

Harris noted that one decisive difference lies in Iran’s failure to separate enemy from neutral traffic; instead the Islamic Republic targeted every vessel that did not first obtain regime permission.

Iranian moves in Hormuz viewed as close to piracy

By firing on ships transiting the strait without legal basis, Tehran came close to the UN definition of piracy, which covers violent acts by one vessel against another, Harris said. The sole difference is that classic piracy involves private actors or mutinous crews; when a state performs the same acts it simply breaches international law.

Additional violations include the March announcement by a senior Revolutionary Guard adviser that only nations friendly to Iran would be allowed passage, breaching the impartiality requirement.

Tehran has also stated its plan to collect roughly 40 billion dollars a year in fees for security, safety and environmental services, and the Persian Gulf Strait Authority has asserted the right to demand insurance purchases before transit.

While fees for actual services rendered may be permissible, Iran cannot charge for safety while itself creating the danger, experts noted.

Harris stressed that a genuine blockade permits stopping and inspecting vessels bound for the adversary but does not authorize firing on them; crews must be allowed to distinguish military from merchant traffic and enemy from neutral destinations.

The contrast, he concluded, is stark: Iranian conduct violates both treaty and customary law, whereas American measures remain within accepted bounds.

No basis for compulsory service charges

Compulsory fees are likewise forbidden, Harris explained. Vessels may be offered services but cannot be forced to accept them. Ships can already use the channel nearer Oman without Iranian assistance, yet Iran has fired on traffic there, undermining any claim that its services are necessary.

The same limit applies to the United States: protection may be offered, but it cannot be made mandatory and then billed to unwilling vessels.

Trump’s earlier 20 percent cargo fee proposal, although later withdrawn, would still have run afoul of the law because protection against piracy is a legal duty, not a commercial option that can be withheld for nonpayment.

After abandoning the fee idea, the former president indicated reimbursement would instead come through trade and investment agreements with Gulf nations.