OMAHA, Neb. (AP) — Union Pacific sued an employee union over what the railroad says was its right to fire an engineer who defecated on a train car connection.

The railroad said in its filing last week in U.S. District Court in Omaha that an arbitrator exceeded his authority in overturning the January 2017 firing of Matthew Lebsack. Omaha-based Union Pacific wants the court to reverse the arbitrator’s finding that the firing was “excessive discipline” and that Lebsack should be reinstated.

The arbitrator said the railroad should have required Lebsack to undergo medical and psychological evaluations and then disciplined him if he were found fit for his work.

Attempts by The Associated Press to reach Lebsack and lawyers for Union Pacific and the Sheet Metal Air, Rail, and Transportation Workers-Transportation Division union were unsuccessful.

Lebsack walked past the locomotive cab bathroom on Nov. 20, 2016, when the train was stopped, according to the lawsuit. He left the locomotive and then defecated on the metal knuckle that connected the locomotive to a trailing rail car. He wiped himself and tossed the soiled tissues out a locomotive window before raising a middle finger twice to a locomotive security camera, the lawsuit says.

It also says he later told his manager that he’d left a “present” for his co-workers.

Lebsack acknowledged at a January 2017 disciplinary hearing that what he’d done was unacceptable and that he was willing to accept responsibility for his actions, the lawsuit says.

The lawsuit doesn’t say where the incident occurred.