French prosecutors have launched an investigation into four fashion retailers suspected of hiding crimes against humanity in China’s Xinjiang region, a judicial source said on Thursday.

According to the source, the cases are related to complaints against China for its treatment of the region’s Muslim minority, the Uighurs, including the use of forced labour.

The source told Reuters that Uniqlo France, a unit of Japan’s Fast Retailing, Inditex, owner of Zara, France’s SMCP and Skechers were being investigated, confirming a report by French media website Mediapart.

“The anti-terror unit has opened an investigation into crimes against humanity following a complaint,” the source said.

Inditex denied the allegations in the complaint, adding that it was carrying out strict traceability checks and cooperating fully with the French investigation.

“Inditex has zero-tolerance for any form of forced labour and we have policies and procedures in place to ensure that such practices do not take place in our supply chain,” the company said in a statement.

SMCP also said it will work with French authorities to prove the allegations are false.

“SMCP works with suppliers around the world and has no direct suppliers in the region that have been reported in the press,” SMCP said, adding that it monitors its suppliers regularly.

Uniqlo France was not immediately available for comment. Skechers said it does not comment on ongoing legal proceedings. The company cited a statement made to Reuters in March 2021 that it applies a strict code of conduct for its suppliers.

In early April, two NGOs sued France against the multinational for covering up forced labour and crimes against humanity.

UN experts and human rights groups estimate that over one million people, mostly Uighurs and other Muslim minorities, have been detained in a vast camp system in the western Chinese region of Xinjiang in recent years.

Many former detainees have reported that they were ideologically trained and mistreated. Human rights groups say the camps are used as a source of underpaid forced labour.

China denies all allegations of abuse.

Many Western brands, including H&M, Burberry and Nike, have boycotted China after concerns were raised about forced labour in Xinjiang.

In March, the US, EU, UK and Canada imposed sanctions on Chinese officials for human rights abuses in Xinjiang. Beijing immediately responded with punitive measures of its own.