EXPLAINER: Trump wants fees for Hormuz just like Iran - is that legal?

President Donald Trump announced that the United States would impose a 20% charge on cargo passing through the Strait of Hormuz after a ceasefire with Iran collapsed, marking a significant shift in Washington's approach to one of the world's most critical shipping routes.

The move follows Iran's closure of the 34-kilometer (21-mile) waterway after U.S. and Israeli strikes on February 28. The Strait of Hormuz serves as the transit route for about one-fifth of the world's oil supplies, as well as other essential commodities, including fertilizers. The closure triggered a global energy shock and renewed concerns over international trade.

Earlier, U.S. Secretary of State Marco Rubio had said that no country had the right to charge vessels for using international waterways, rejecting Iran's proposal to collect transit fees. However, Trump had previously suggested that the United States could impose charges if negotiations with Iran failed.

In a social media post on Monday, Trump declared that the United States would become the "Guardian of the Hormuz Strait" and said all cargo passing through the waterway would be subject to a 20% charge as reimbursement for providing security in the region.

Trump did not explain how such charges would be enforced or identify the legal authority that would allow the United States to collect them.

Iran, meanwhile, maintains that control over the Strait of Hormuz remains a key part of its national security strategy. Tehran argues that a temporary agreement reached last month recognized its role in ensuring safe passage through the waterway for a limited period.

The United States has interpreted that agreement differently, saying it only required Iran to facilitate safe navigation without imposing restrictions or using force.

During the conflict, Iran established the Persian Gulf Strait Authority and required vessels passing through the Strait to coordinate with Iranian authorities. Tehran has also insisted that ships travel closer to the Iranian coastline and has intercepted vessels that navigated near Oman's waters without prior approval. Although Iran has suggested it may eventually introduce transit fees, it has not released details of any proposed charges.

Under the United Nations Convention on the Law of the Sea (UNCLOS), countries bordering international straits generally cannot charge vessels simply for exercising their right of passage. Limited fees are permitted only for specific services, such as pilotage, towing, or port operations, and must be applied without discrimination.

Although neither the United States nor Iran is a party to UNCLOS, the convention is widely regarded as the basis of international maritime law, and the Strait of Hormuz is generally recognized as an international waterway.

Shipping industry officials said no country has unilaterally imposed transit charges on an international strait in modern history.

Oman has continued discussions with Iran and has allowed vessels to pass through its territorial waters without charging transit fees.

The proposal has raised concerns among Gulf nations, whose energy exports rely heavily on the Strait of Hormuz, as well as major global importers of oil and fertilizers. Analysts warn that a 20% surcharge on cargoes could significantly increase shipping costs and drive global oil prices higher. -Reporting by Jonathan Saul; Additional reporting by Jonathan Spicer; Writing by Angus McDowall; editing by Barbara Lewis, Kirsten Donovan/Reuters