Uber Technologies is the subject of a U.S. Department of Justice criminal investigation that is probing the company's use of a software tool that helped drivers avoid transportation regulators when encroaching into areas where the service wasn't approved, Reuters has reported.

The tool, called "Greyball," would use data from the Uber app, including user payment information, to identify law enforcement and deny ride requests to those individuals if they requested a pick-up in a region where Uber cars were banned or under scrutiny. 

The New York Times reported on the existence of Greyball earlier this year. In a statement to the Times, Uber acknowledged the tool, explaining that it was developed to help the company weed out people who might be misusing its service, including competitors, opponents, and individuals intent on harming drivers.

It is not clear what federal laws use of this tool may have potentially violated. An Uber spokesman and the Justice Department declined to comment, Reuters further reported. In late April, a Portland Bureau of Transportation audit report noted that a California-based U.S. attorney had launched a federal inquiry into Greyball, but the report did not specify whether or not it was a criminal investigation.

On March 8, Uber announced in a blog post that it would no longer allow use of the tool to elude local regulators.