Multinational retailers are fighting back after authorities in France launched an investigation into the supply chain activities of Uniqlo, Zara-owner Inditex and SMCP, a French textile firm.

French prosecutors are conducting a probe of the firms and footwear brand Skechers because they source their products from China’s Xinjiang region, French investigative journal Mediapart reported.

The investigation comes after activists with the Uyghur Institute of Europe, a Uyghur individual and anti-corruption group Sherpa filed a complaint alleging the retailers were profiting from forced labor, the report said.

“We strongly refute the claims in this complaint,” an Inditex spokesperson said, according to television reports.

“Inditex conducts rigorous traceability controls and we intend to fully cooperate with the French authorities to confirm that the allegations are unfounded.

“At Inditex, we have zero tolerance for all forms of forced labor and have established policies and procedures to ensure this practice does not take place in our supply chain.”

Uniqlo’s parent company, Fast Retailing, in Tokyo, said the firm will “cooperate fully with the investigation to reaffirm there is no forced labor in our supply chains.”

Sophie Richardson, China director at Human Rights Watch, told the BBC that multinational corporations conduct audits of supply chains, but because “political repression in the Xinjiang region is so pervasive, labor inspectors cannot interview workers freely without fear of reprisals.”

Companies that have raised concerns regarding forced labor in Xinjiang, including Nike, H&M and Burberry, have been subjected to informal boycotts in China, a major market for their goods.

Concerns regarding human rights abuses in Xinjiang have stopped cargo and prompted complaints from U.S. importers as U.S. Customs and Border Protection step up enforcements that delay shipments.

Uniqlo USA had a shipment of men’s shirts stopped early this year. Retailers overall are being required to provide more proof ahead of shipments, showing products are free from forced labor, the Wall Street Journal reported on Monday.