The United States' customs agency blocked a shipment of Fast Retailing Co.’s Uniqlo shirts in January for violating an order prohibiting imports of items suspected to be produced by forced labor from China’s state-owned Xinjiang Production and Construction Corps.

The blockage of Uniqlo’s cotton men’s shirts, which happened at the Port of Los Angeles, was revealed in a U.S. Customs and Border Protection document dated May 10 in which the agency denied an appeal by Uniqlo to release the shirts. Uniqlo is the main brand of Asia’s largest apparel retailer, Fast Retailing, and founded by Tadashi Yanai.

The U.S. customs document notes that Uniqlo had argued and provided proof that the raw cotton used to produce the shirts didn’t originate from Xinjiang Production and Construction Corps. Still, Uniqlo failed to provide enough information to establish the items were not produced in part by forced labor in China’s far west Xinjiang region, according to the customs agency.