In the letters sent Tuesday, Wyden asks whether the car companies maintain a list of “foreign-language names” of suppliers. He’s also seeking the names of their five largest so-called Tier 1 suppliers — which provide parts directly to the automaker — that have direct or indirect sub-suppliers in China.

“Information I have learned from the initial stages of the Committee’s investigation raises serious questions about Tier 1 suppliers’ ability to ensure that sub-suppliers do not rely on forced labor,” Wyden wrote to suppliers including Denso Corp., Continental AG, Magna International Inc., ZF Friedrichshafen AG and Robert Bosch GmbH. 

In his letter to the automakers, which also included Ford Motor Co., Stellantis, Mercedes-Benz USA LLC, American Honda Motor Co. Inc. and Volkswagen Group of America Inc., Wyden cited a report by Sheffield Hallam University that highlighted links between Chinese companies with operations in Xinjiang and automakers using metal, batteries, wiring and wheels made there. The letter asked for responses by April 11.