A recent US customs ruling has thrown the global gold trade into turmoil, prompting major suppliers to halt shipments to the United States. The confusion over whether certain gold bars will face steep import tariffs has put one of the world’s most important commodity flows on pause.

Some of the most widely used types of gold bars would be subject to U.S. tariffs, customs agency officials ruled, a particular blow to Switzerland’s large gold refining industry.

A Trump administration ruling that gold bars will be subject to tariffs stunned traders who had assumed they would be exempted, throwing bullion markets into turmoil.