U.S. government investigators have interviewed workers at Goodyear Tire & Rubber Co’s (GT.O) Malaysian factory about their working conditions, employees told Reuters, intensifying scrutiny of potential labour abuses by the tyre maker in the country.

The questioning by the Department of Homeland Security could lead to U.S. prosecutions of one of the world’s biggest tyre makers, which faces related lawsuits and two ongoing investigations by regulators in Malaysia and the United States, each looking into potential exploitation of foreign workers.

Five current and former Goodyear Malaysia staff said Homeland Security Investigations (HSI) agents have asked about their working and living conditions, details of court cases they filed against Goodyear, a police complaint alleging threats from Goodyear staff and workplace accidents.