The U.S. Justice Department has contacted the Philadelphia Parking Authority in connection with a probe into software Uber used to avoid enforcement when the service was illegal in the city.

The Parking Authority's spokesman, Martin O'Rourke, confirmed contact with the Justice Department on Friday. He did not indicate what software is the focus of the federal authorities' inquiry, but officials in Portland, Ore., revealed in an April audit that the city had been notified by the U.S. Attorney's Office of the Northern District of California that Uber's use of a software tool called Greyball was the subject of a federal criminal inquiry.

In a statement Friday, a commissioner from Portland's Bureau of Transportation, Dan Saltzman, said his office would "support the criminal investigation by the United States Department of Justice into Uber's use of the Greyball tool to evade regulators."

Officials in Portland and Philadelphia said they are cooperating with federal authorities.

The U.S. Attorney's Office of the Eastern District of Philadelphia did not reply to a request for comment.

While ride hailing companies such as Uber and Lyft now operate legally in Philadelphia, that was not the case for about two years. When Uber debuted in the city in 2014, it was illegal, and the PPA sought to ensnare drivers in stings and fine them. Uber fought back. In 2015, the PPA complained that Uber had technology to flag internet addresses and cellphone numbers that had been used in previous stings and ensure that requests for service made from those sources would be blocked.

According to New York Times reports on Greyball, blocking those numbers was just the tip of the iceberg. That paper reported in March that Uber went to great lengths to target cellphones it identified as potentially connected to enforcement efforts and created a fake version of the app for those devices. Use of the Greyball tool extended around the world, from Boston to Paris, and to Australia and China.

Uber declined to comment on federal officials' contacting the PPA, and referred to a statement issued in March about "greyballing."

The technology, the company said, was used to test new features, prevent fraud, protect drivers from physical harm, and deter passengers who violate the company's terms of service.

The statement also said Uber would prohibit the use of the software to block action by local regulators.

In the 2016 agreement between Uber and the PPA that legalized the company's services, Uber agreed to reinstate all credit cards and telephone numbers that had been blocked by the company because the PPA used them to police the then-rogue ride hailing service.