The Department of Justice has filed a class-action lawsuit against American Airlines, claiming the carrier illegally denied benefits to pilots while they were serving in National Guard and reserve units.

The Department of Justice said Thursday night that it filed the lawsuit in U.S. district court in Dallas on behalf of three Naval Reserve and Air National Guard pilots.

Officials said it was the first time they had filed a class-action case charging an employer with violating a 1994 law designed to protect employees who leave their jobs temporarily to serve in military units.

The government charged that American conducted an audit in 2001 and cut benefits of pilots who took leave for military service but didn't reduce benefits of pilots who took other types of leave.

"No reservists - indeed, no members of our armed forces - should ever be punished or discriminated against for answering the call of duty," said Wan J. Kim, assistant Attorney General for civil rights.

Tim Wagner, a spokesman for American Airlines, declined to comment on specifics of the lawsuit.

Wagner said many pilots come out of the military and have obligations for further service. "We are committed to doing our best to help them do their duty to their country," he said.