OMAHA, Neb. (AP) — Union Pacific has sued an employee union over the railroad’s 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.

The lawsuit says Lebsack walked past the locomotive cab bathroom on Nov. 20, 2016, when the train was stopped. It says he left the locomotive and defecated on the metal knuckle that connected the locomotive to a rail car. The lawsuit says he then tossed soiled tissues out a locomotive window and raised a middle finger twice to a security camera.

It also says he later told his manager that he’d left a “present” for his co-workers. The lawsuit doesn’t say where the incident occurred.