Eight of the world’s largest shipping industry associations urged the United Nations and International Maritime Organization to oppose any compulsory tolls or transit charges in the Strait of Hormuz, warning that such a move could set a precedent for similar fees at other key maritime choke points.

In a joint letter dated August 3 to UN Secretary-General António Guterres and IMO Secretary-General Arsenio Dominguez but published on August 5, the groups said introducing transit tolls or service fees “that are a toll in all but name” would undermine the international legal framework governing navigation through international straits.

“Once such a precedent is established, it becomes increasingly difficult to resist similar measures elsewhere, creating uncertainty for international shipping and global commerce,” wrote the group, which included the International Chamber of Shipping, BIMCO, the World Shipping Council and others.

The prospect of Iran imposing transit fees in Hormuz has focused attention on the fragility of global supply chains and raised concerns over how maritime choke points could be managed in future.

Tehran has moved to tighten its control over traffic through the strait since the U.S. and Israel began strikes on the country in late February, warning ships that they need the Islamic regime’s permission to transit the choke point, and threatening to impose permanent transit fees or mandatory insurance requirements. Iran has even sought payments of as much as $2 million per voyage on an ad-hoc basis.

Before the war, ships transited the waterway largely unimpeded. Since then, the U.S. has resisted Iran’s attempts to assert control, backing a southern route adjacent to Oman and deploying forces to help safeguard commercial vessels using the corridor.

Still, U.S. President U.S. Donald Trump in July briefly floated imposing a 20% charge on cargo shipments crossing with U.S. assistance, only to back away from the plan after allies in the Gulf urged him to drop it.  

Meanwhile, Oman has told the IMO that it opposes mandatory transit charges in the strait. It has, however, indicated openness to examining voluntary agreements where ships could contribute to navigation support services aimed at improving maritime safety, security and environmental protection.

“As discussions regarding regional security and conflict resolution take place, we must ensure that internationally recognized rights of navigation are not compromised or used as part of broader political negotiations,” the shipowners wrote in the letter.

The U.S., Iran and Oman are nearing a 60-day agreement on shipping through Hormuz that would involve no tolls or fees, Axios reported on August 3, though it’s unclear what would happen after that time period.