The U.S. government filed a lawsuit on Monday accusing United Airlines Inc of violating a pilot's employment rights by failing to provide sick leave when he was called to active duty by the U.S. Air Force, where he was a reservist.

According to a complaint filed in Chicago federal court, United failed to credit Lieutenant Colonel Daniel Fandrei with sick leave while he was deployed as a KC-10 pilot in southwest Asia from December 2012 to March 2013.

The U.S. Department of Justice said the Chicago-based carrier did this despite offering such benefits to other employees on similar leave, violating the federal Uniformed Services Employment and Reemployment Rights Act (USERRA).

"USERRA ensures that service members like Lt. Col. Fandrei who answer our nation's call to duty don't return to civilian life and find their employment benefits denied and their civil rights violated," Vanita Gupta, head of the Justice Department's civil rights division, said in a statement.

In a statement, the carrier said it believes its policies comply with USERRA, and that it is "committed to supporting the many aviation professionals at our airline who served or who are currently serving in the military."

United's parent is United Continental Holdings Inc.

The lawsuit seeks to recoup the value of Fandrei's lost benefits, and an injunction against similar violations.

It is part of the U.S. government's effort to ensure that military personnel are not penalized for serving their country, including legal actions to stop improper home foreclosures and car repossessions.

The Justice Department said Fandrei, of Fairfield, California, worked at the time of his deployment for Continental Airlines, whose contract with its pilots did not let them accrue sick leave during military deployments.

United and Continental had merged in 2010.

According to the complaint, Fandrei was commissioned as an Air Force officer in 1990, and retired from the Air Force Reserve as of Jan. 1, 2016.

He joined United as a pilot in 2000, and was recalled from a furlough six months before being deployed, the complaint said.

(Reporting by Jonathan Stempel in New York; Editing by Tom Brown and Diane Craft)