China has halted exports of critical minerals and ores to the US—and which are important to automakers, aerospace manufacturers, semiconductor companies, and defense contractors around the world, reports The New York Times.

Shipments have been halted at many Chinese ports as the Chinese government develops a new regulatory system. Once implemented, the new system could permanently disrupt supplies to some companies, including American military contractors.

On April 4, the Chinese government ordered export restrictions on six heavy rare earth metals that are completely mined in China, as well as rare earth metals, 90 percent of which are produced in China.