Ridesharing service Uber has reportedly threatened to fire one of its top self-driving engineers, Anthony Levandowski, if doesn’t cooperate with an ongoing investigation into allegations that he stole trade secrets from his former employer Waymo.

Uber’s ultimatum forcing Levandowski to cooperate with the investigators became public recently when the executive’s lawyers filed fresh documents with the court, demanding Judge William Alsup to modify the order in which Uber directed to ask Levandowski to comply with the legal investigation.

In that order, the judge had also given Uber a deadline of May 31 to return the allegedly stolen material to Waymo.

Levandowski's lawyer argued, “When court orders an employer to do everything in its power to force an employee to speak, cooperate, and discard his Fifth Amendment rights, the threat of termination is not the mere discretionary choice of a private employer.”

Waymo, Google parent Alphabet’s self-driving car unit, filed a lawsuit against Uber earlier this year, claiming it is using stolen autonomous technology. As per the lawsuit, Levandowski downloaded thousand s of files from the company’s servers and resigned to start his own business Otto, which was eventually bought by Uber.