WICHITA (AP) – The technical and engineering union for Spirit AeroSystems says it’s preparing to file a lawsuit in an effort to obtain an outside arbitrator.

The Wichita Eagle reports that the union alleges Spirit refuses to honor the grievance process from a dispute over changes to the employee rating system.

The Society of Professional Engineering Employees in Aerospace represents 900 Spirit AeroSystems engineers and technical workers in its bargaining units.

The union says Spirit is refusing to honor the contractual grievance process. It says that under the process, disputes regarding alleged violations of bargaining agreements typically go to an independent arbitrator for a final judgment.

Spirit AeroSystems spokesman Ken Evans says it would be unfortunate if SPEEA chooses to take legal action and stressed that Spirit “values” its labor unions.