SAN FRANCISCO (Reuters) - Alphabet Inc’s Waymo self-driving car unit asked a U.S. judge on Monday to postpone an upcoming trade secrets trial against Uber Technologies Inc, so Waymo could investigate whether Uber withheld important evidence in the case.

Slideshow ( 3 images )

The trial is currently scheduled to begin on Dec. 4 in San Francisco federal court. Waymo said it learned of new evidence last week after the U.S. Department of Justice shared it with the judge overseeing the case.

The two companies are battling to dominate the fast-growing field of self-driving cars.

In its court filing on Monday, Waymo said it recently learned that a former Uber [UBER.UL] security analyst sent a letter to an Uber in-house lawyer more than six months ago, which contained important facts about the case.

Waymo’s court filing is partially redacted from public view, so the details of the analyst’s letter are unclear. However, Waymo said Uber concealed the letter despite demands from Waymo and the judge to disclose all relevant evidence.

“Uber has been waiting for its day in court for quite some time now,” an Uber spokeswoman said. “We’re keen to have a jury finally hear this case on its merits.”

Waymo sued Uber in February, claiming that former Waymo executive Anthony Levandowski downloaded more than 14,000 confidential files before leaving to set up a self-driving truck company, called Otto, which Uber acquired soon after.

Uber denied using any of Waymo’s trade secrets. Levandowski has declined to answer questions about the allegations, citing constitutional protections against self-incrimination.

Earlier this year U.S. District Judge William Alsup, who is hearing the civil action brought by Waymo, asked federal prosecutors to investigate whether criminal theft of trade secrets had occurred. That probe is being handled by the intellectual property unit of the Northern California U.S. Attorney’s office, sources familiar with the situation said. No charges have been filed.

Alsup disclosed last week that he had received a letter from prosecutors, which he did not reveal. However, Alsup ordered the former Uber security analyst, the Uber in-house lawyer and another witness to appear in court on Tuesday at a final pretrial conference.

It is unusual for prosecutors to share information with a judge days before a civil case is set to begin. Alsup already delayed the trial once before, in October, citing Waymo’s need to probe separate evidence Uber had not promptly disclosed.

Uber in the last year has been hit by scandals, including accusations of sexual harassment and federal criminal probes into software the ride-hailing firm used to deceive regulators and allegations it paid bribes to authorities in Asia.

The latest controversy to hurt the firm’s reputation is last week’s revelation that Uber tried to cover up a 2016 data breach that impacted about 57 million customers.