Jan 12 (Reuters) - The United States" Congressional-Executive Commission on China (CECC) released a letter to the International Olympic Committee (IOC) on Wednesday voicing concern over forced labour in the production of uniforms ahead of the Beijing Games. The CECC is concerned that Anta Sports and Hengyuanxiang Group (HYX Group), with which the IOC has contracts to produce uniforms, use cotton from the Xinjiang Uyghur Autonomous Region (XUAR). "Cotton produced in the XUAR is synonymous with forced labor and the systematic repression that takes place there," the letter said. "Forced labor plays an integral role in the genocide taking place against Uyghurs and other predominantly Muslim ethnic groups in the region." The IOC did not immediately respond to a request for comment. The U.S. government and many rights groups say Beijing is carrying out genocide in Xinjiang. China denies the allegations of human rights abuses. read more "Because Anta and HYX Group both continue to use cotton produced in the XUAR, there is a worrisome possibility that IOC personnel or others attending the 2022 Olympic Games will be wearing clothing contaminated by forced labor," the CECC added in the letter. Among the commission"s requests of the IOC were to make public a "certificate of origin" that HYX Group provided the IOC "that reportedly confirmed that no forced labor was used" in its production. The CECC also asked the IOC to explain publicly "assurances" from Anta Sports that its products were not produced through forced labor. The Winter Olympics run from Feb. 4-Feb. 20.