The U.S. Justice Department appears to be probing Uber’s use of software to avoid regulators

The U.S. Justice Department appears to have opened an investigation into Uber following reports that the ride-hailing company used a special tool to evade regulators and law enforcement officials around the country.

In cities like Portland, Ore., where Uber previously did not have permission to operate, the company in 2014 had relied on software known internally as “Greyball” to identify government officials and prevent them from booking rides. The New York Times first revealed Uber’s practice this March, leading the tech giant days later to say it would not use the system — originally designed to detect fraud — to avoid scrutiny.

In their report on Uber’s behavior, however, Portland officials indicated last week that they had been notified by the U.S. Attorney in the Northern District of California that “Uber is the subject of a federal inquiry.” A report from Reuters on Thursday said the company specifically had received a subpoena from a grand jury there, meaning that the DOJ’s investigation is likely criminal in nature.

Uber declined to comment. A spokesman for the Justice Department did not immediately respond to questions about a federal probe.

For its part, Uber confessed to Portland officials in an April 21 letter that it had used “Greyball” to mask its UberX drivers over a two-week period in December 2014, when the company did not have permission to operate UberX in the city. The company suspended its operations there shortly after.

After it gained the green light in April 2015, however, Uber said it ceased “greyballing” regulators.

“While our investigation is ongoing and we will inform the City if this conclusion changes, our review indicates that Uber has not used the Greyball technology with respect to regulators in Portland at any time during or since the implementation of Portland’s [Transportation Network Company] regulations and pilot program in April 2015,” Uber wrote. “In fact, our review indicates that Uber has not used the technology in Portland since April 2015 for any reason.”

Here are the letters Uber sent to Portland officials:

This article originally appeared on Recode.net.