The Trump administration is extending a waiver of U.S. shipping rules for another 90 days as it looks to keep gasoline and other fuel costs in check, the White House said Monday.

The waiver temporarily relaxes requirements under the Jones Act, the century-old law that requires shipping between U.S. ports to be carried out by American ships.

“Today, the Trump Administration issued a 90-day extension to the Jones Act waiver to ensure our military and key industries maintain uninterrupted access to critical resources,” White House spokesperson Taylor Rogers said in a statement.

The administration first issued a waiver in March allowing foreign ships to move products between U.S. ports. It announced an extension in April as the war in Iran pushed up fuel and other commodity prices.

The conflict has disrupted shipping through the Strait of Hormuz, a major chokepoint off Iran’s coast, putting additional pressure on energy prices.

U.S. drivers are already paying considerably more at the pump. The national average for a gallon of gasoline was about $4.01 on Monday, according to AAA, roughly 87 cents higher than at the same time last year.

The waivers have drawn pushback from the domestic shipping industry, and the White House is narrowing the latest extension.

It will apply only to certain commodities, including gasoline, diesel, crude oil, petrochemicals, natural gas and fertilizer.

The Defense Department will also have to consult with the U.S. Maritime Administration to determine whether Jones Act-compliant vessels are available before deciding whether the waiver applies to an individual voyage.

How much the move could lower prices is less clear. Past estimates suggest the effect could be relatively small. In 2022, JPMorgan projected that a Jones Act waiver could save East Coast drivers about 10 cents per gallon, according to Bloomberg.

The White House, however, says the previous waivers have already helped move more fuel and other essential products between U.S. ports. An administration official said the changes allowed for an increase of as much as 50 percent in domestic shipments.

“Data shows the waiver has driven a significant increase in domestic deliveries of essential products such as gasoline, diesel, and jet fuel. President Trump continues to take bold, commonsense action that protects and strengthens America’s economic and national security,” Rogers said.