TOKYO: Fast Retailing Co Ltd's Uniqlo brand shirts were blocked at the United States border in January on concerns they violated a ban on cotton products produced in the Xinjiang region of China, where there have been reports of forced labour.

A U.S. Customs document dated May 10 said a shipment of Uniqlo men's shirts was impounded on Jan. 5 at the Port of Los Angeles due to a suspected violation of the ban. The document said a protest filed by Uniqlo's parent company was denied.

Representatives of Fast Retailing did not immediately respond to request for comment.