The Trump administration is tacking on new, costly fees to special, foreign-made ships that transport cars in and out of American ports.

Hundreds of thousands of vehicles a year are imported and exported on ships that resemble floating parking garages. These carriers, known as roll-on, roll-off vessels, or ro-ros, are primarily manufactured in China, Japan and South Korea. Some can hold up to 9,000 vehicles.

The administration wants to revive shipbuilding in the United States and dent China’s position as the world’s dominant shipbuilder. To do that, it introduced rules this year that require Chinese-built and Chinese-owned ships to pay high fees when they visit U.S. ports.

However, the rules go much further with ro-ros, forcing all foreign-built vehicle carriers to pay the fees, not just those built in China, regardless of whether they’re bringing vehicles into the country or shipping them out.

The companies that operate and use the carriers say the rules will burden them with new costs and add as much as $300 to the price of a car. They also say they are confused by the stricter approach for such an essential part of the supply chain.

“We don’t have a crystal ball into why that arrived, or why ro-ros were focused on to any extent at all,” said Mark Vlaun, the vice president of government relations at American Roll-On Roll-Off Carrier, a vehicle carrier operator.