ROME (AP) — Italian prosecutors have asked 13 luxury fashion firms to provide documents on governance, internal controls and audits as part of an investigation into the alleged exploitation of Chinese workers at subcontractors, judicial documents showed on Thursday.

According to the documents obtained by The Associated Press, the investigation highlighted episodes of “heavy exploitations” of Chinese workers at subcontractors’ workshops, where the brands involved produced some of their products.

The 13 fashion firms didn’t immediately comment on the prosecutors’ requests and allegations.

The fashion companies that received the orders are: Dolce & Gabbana, Versace, Prada, Adidas Italy, Missoni, Ferragamo, Givenchy Italia, Alexander McQueen Italia, Gucci, Yves Saint Laurent Manifatture, Pinko, Coccinelle and Off-White Operating.

Milan prosecutors will use the requested documents to verify the level of involvement of the brands in the workers’ abuse and the possible consequent measures, the documents said.

The probe is the latest in a string of police operations and investigations revealing the abusive treatment of sub-contracted workers by high-end brands.

Last month, Milan prosecutors placed luxury group Tod’s and three of its executives under investigation for suspected labor abuses and exploitation, also requesting a six-month ban on the company’s advertising. Tod’s denied any wrongdoing.

In April, Italian police disclosed that Chinese workers employed by an unauthorized subcontractor, produced handbags and accessories for Giorgio Armani.