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By Dan Levine and Joseph Menn

(Reuters) - The city of Portland, Oregon plans to subpoena Uber Technologies Inc to force it to disclose software that helped its drivers evade local transportation regulators, a city official said on Friday.

Uber has acknowledged using the software, known as Greyball, to circumvent government officials who were trying to clamp down on Uber in areas where its service had not yet been approved, including Portland. It has since stopped the use of the software for that purpose, saying the program was created to check ride requests to prevent fraud and safeguard drivers

Reuters reported on Thursday that the U.S. Department of Justice has begun a criminal investigation into Uber's Greyball program, and that a Northern California grand jury had issued a subpoena to Uber concerning how the software tool functioned and where it was deployed.

Portland began its own investigation of Greyball after the New York Times revealed its existence in March. Uber has shared some information with the city but has not turned over the Greyball software itself.

In an interview on Friday, Portland Commissioner Dan Saltzman, who oversees the city's transportation department, said his colleagues on the city council have pledged to support a subpoena against Uber, which will be voted on next week. If Uber does not comply, Portland could ultimately review its ability to operate in the city, Saltzman said.

"We are not ready to go there yet," Saltzman said.

In a statement, Uber's general manager for Oregon Bryce Bennett said the company has "fully cooperated" with Portland and provided relevant information to its investigation. The city said it found no evidence Uber used Greyball to avoid inspectors since Uber was allowed to operate there in 2015.

Portland received its own subpoena from the Northern California grand jury for records relating to Uber's activities, including emails between the city and the company or its representatives, according to a copy of the document reviewed by Reuters.

The subpoena to Portland was issued on March 10, a week after the New York Times report.

The Portland subpoena does not indicate what criminal laws are at issue in the probe. Likewise, Uber's grand jury subpoena does not list any federal statutes that may have been violated, a source familiar with the document said.

A subpoena from a grand jury is a request for documents or testimony concerning a potential crime. It does not, in itself, indicate wrongdoing or mean charges will be brought.