A lawmaker announced a proposal on Thursday that would compel counties to pay transit fees when passing through the Strait of Hormuz, highlighting Iran’s growing leverage over one of the world’s most vital waterways, which carries roughly one-fifth of global oil and liquefied gas traffic.

Since the outbreak of the U.S.-Israeli conflict with Iran, Tehran has been blocking passage through the strait for vessels it associates with its adversaries and their allies. The proposed legislation would extend this pressure into an economic tool, applying tolls and taxes to countries using the route for shipping, energy, and food transport.

An adviser to Iran’s supreme leader signaled that once the war ends, a new governance framework for the strait would be established, giving Tehran the power to impose maritime restrictions on nations that have sanctioned it. Senior official Mohammad Mokhber was quoted as saying that Iran could effectively use the strait’s strategic position to block Western shipping as a form of counter-sanction.