A demonstrator holds a placard as activists demonstrate outside the Colosseum, calling on G-20 leaders to boycott the Beijing 2022 Winter Olympics due to China’s treatment of Tibet, Uyghur Muslims and Hong Kong, in Rome, Italy, Oct. 29, 2021.

U.S. lawmakers from both parties have written a letter to International Olympic Committee President Thomas Bach inquiring about the group’s links to two Chinese companies using cotton from China’s Xinjiang province to make its uniforms.

China is accused of carrying out genocide and forced labor against the province’s large Uyghur Muslim population. It denies the accusations.

The letter states cotton from Xinjiang “is synonymous with forced labor and the systematic repression that takes place there.”

“There is a worrisome possibility that IOC personnel or others attending the 2022 Olympic Games will be wearing clothing contaminated by forced labor,” the Congressional-Executive Commission on China, or CECC, wrote.

The letter, signed by CECC chairman Senator Jeff Merkley and co-chair Representative James P. McGovern, as well as Representative Christopher Smith, a ranking member, specifically states that two companies, Anta Sports and the textile company Hengyuanxiang (HYX) Group, use Xinjiang cotton.

In the letter, the lawmakers asked the IOC to show the certificate of origin they were given from HYX Group. They also have asked the IOC to “explain the assurances” they were given from Anta Sports about their cotton products.

“As a starting point to fulfilling its commitment to uphold and respect human rights, and in line with the preservation of human dignity enshrined in the Olympic Charter, the IOC must uphold and respect the human rights of those who made the uniforms on their backs,” the letter concludes.

In December, President Joe Biden signed the Uyghur Forced Labor Prevention Act, which bans all imports from Xinjiang into the United States unless companies can show the U.S. government “clear and convincing evidence” their supply chains have not used the labor of ethnic Muslims enslaved in Chinese camps.