A French prosecutor’s office started the investigation last month looking at accusations that Claudie Pierlot parent SMCP SA, Zara owner Inditex SA, Skechers and Uniqlo profited from human rights crimes against the Muslim ethnic group, according to an official from the French Prosecution Office. It follows a joint complaint filed in April by various parties including non-governmental organizations, Sherpa and Ethique sur l’etiquette.

The probe from the Parquet national anti-terroriste shows how a campaign to raise awareness about the plight of the Uyghurs in China has gained traction in Europe. Western fashion brands have been heavily criticized in their home markets for trying to maintain business as usual in China despite allegations that the government is forcing Uyghurs and other minorities to work against their will.

For its part China has denied the allegations, saying they’re an attempt to undermine successful businesses and it accuses brands of spreading false information amid a rise in nationalistic sentiment in the world’s second biggest economy. The Xinjiang region produces more than 80% of the country’s cotton.

SMCP and Inditex both strongly denied the accusations and said they will fully cooperate with the French investigation. Inditex said that traceability controls are carried out “rigorously” on their clothing.

While Uniqlo’s parent Fast Retailing said it’s aware of the report on the probe, but hasn’t been contacted by authorities.

“If and when notified, we will cooperate fully with the investigation to reaffirm there is no forced labor in our supply chains,” the company said in a statement. Skechers declined to comment on pending litigation.

The campaign is being backed by Raphael Glucksmann, a European Member of Parliament who described the decision to open a probe as “historic.”

“Multinationals have long been above the laws. We’re going to show them the rule of law applies to all, even the wealthiest and most powerful,” he tweeted Thursday. “This probe is a key moment in a wider battle.”

The legal complaint was lodged in April by human rights lawyer William Bourdon on behalf of the NGOs as well as the European Uyghur Institute.

Earlier this year, some Western brands such as H&M were targeted by calls for boycott from Chinese social media after the Swedish fast-fashion brand published a statement about concerns over forced labor allegations in the Xinjiang in China.