The U.S. State Department sent a warning to major U.S. companies about the risks to supply chains from human rights abuses against Uighur minorities in China’s Xinjiang region.

“It is critical that U.S. companies and individuals be aware of the large-scale human rights abuses perpetrated by the PRC government [CCP] in Xinjiang,” Keith Krach, assistant secretary of state for economic growth, energy and the environment, wrote on July 1 in a letter reviewed by Reuters.

Among the companies listed in the State Department’s letter are Walmart, Apple Inc., and Amazon.com Inc. The warning is part of the ongoing U.S. pressure on the Chinese Communist Party (CCP) and its role in perpetrating human rights violations against Muslim Uighurs in the Xinjiang region, Falun Gong practitioners, and Christian minorities.

“Businesses should evaluate their exposure to the risks that result from partnering with, investing in, and otherwise providing support to companies that operate in or are linked to Xinjiang,” the letter to the business groups said.

On Wednesday, the U.S. government also issued a warning that companies doing business with Xinjiang or entities using Xinjiang labour would be exposed to reputation, economic, and legal risks.

Because of the complex nature of supply chains, Krach noted that companies were susceptible to potential risks, and urged more attention. “It’s incumbent on the board of directors for each company to conduct a detailed analysis of their supply chains to reveal who their company is buying from and who it is selling to,” he said.

Just last Wednesday, the Customs Protection Agency (CBP) announced the seizure of a shipment of human hair extensions in New York from China on suspicion that they belonged to people held in Xinjiang’s internment camps.

The beauty products had a value of approximately $800,000 and there are “potential indicators of human rights abuse, forced child labour, and deprivation of liberty,” Customs spokesman Anthony Bucci told EFE.

According to United Nations estimates, more than 1 million Muslims have been held in detention camps in Xinjiang.

As Business Insider pointed out, the CCP has denied mistreatment and said the camps provide vocational training and help combat extremism.