Uber received a subpoena from a grand jury in Northern California, which has sought documents concerning how the software tool functioned and where it was deployed, suggesting that a criminal investigation is in progress, reported Reuters on Thursday, citing two persons familiar with the situation.
After the New York Times revealed Greyball's existence in March, Uber vowed to stop using it to evade authorities.
A Justice Department spokesman and an Uber spokesman declined to comment.
Uber previously said the software was created to catch riders who violated its terms of service, including "people aiming to physically harm drivers, competitors looking to disrupt our operations, or opponents who collude with officials on secret "stings" meant to entrap drivers".
Uber had used Greyball software to intentionally evade the agency's officers from December 5 to December 19, 2014 and deny 29 separate ride requests by its enforcement officers, according to the PBOT investigation initiated after the New York Times report on greyballing technology.
These include an internal investigation into sexism and sexual harassment claims, a damaging #UberDelete campaign, use various tools to gain a competitive edge and a fierce legal battle with Alphabet's self-driving unit Waymo.
The federal probe into the San Francisco-based company is far from being completed and there's now no indication of whether there's a realistic chance that Uber ends up facing criminal charges for its potentially illegal practices. That indicates a criminal investigation is underway.
"Greyballing" was extensively used in cities where Uber services were either restricted or banned outright, according to the report.
"This program denies ride requests to users who are violating our terms of service".
Uber has admitted that the software aided its drivers in identifying and avoiding transport regulators in certain areas where the firm has not yet been approved for use. Social-media, G.P.S., and credit-card information that traced back to police unions were all used to make sure authorities were shown fake cars on their Uber app and drivers would quickly cancel rides.
The city said it found no evidence that the behavior was repeated when Uber re-entered the market in April 2015.