WASHINGTON, DC - WMATA GM Paul Wiedefeld (Bill O'Leary/The Washington Post)

Metro filed a federal lawsuit Friday challenging its employees’ union in an ongoing dispute about overtime.

Metro employees who work on a day off are paid at time-and-a-half, and employees who work on a second, consecutive day off — what is called the “seventh day” — are paid double time.

An arbitrator ruled last year that employees with seniority can choose to work seven days and earn double time pay. The ruling found they are entitled to do so under the terms of their collective bargaining agreement with the transit agency.

But Metro is arguing that the provision of the contract makes no concession to “potential fatigue.” The agency has been paying “certain employees not to work on their seventh day” in the name of safety.

Now, Metro’s lawsuit seeks to vacate the arbitrator’s ruling, which would free it from the obligation to accommodate employees who want to work seven days in a row.

The “[Washington Metropolitan Area Transit Authority] has a compelling public policy interest underlying its decision to promote the interests of safety for its riders and its employees,” according to the lawsuit, filed in U.S. District Court in Eastern Virginia. “ … In spite of this compelling public policy interest, the Arbitrator impermissibly ordered WMATA to require employees who are otherwise eligible for overtime to work on a seventh consecutive day.”

In a statement, Metro General Manager Paul J. Wiedefeld defended the legal action.

“Metro must be in a position to enforce safety policies for its employees,” he wrote, adding that the agency has an obligation to protect employees and passengers.

However, the Amalgamated Transit Union Local 689, which represents Metro employees, said Metro’s fatigue policies are not consistently applied.

Esker Bilger, the union’s financial secretary-treasurer, said Metro recently forced employees to work during the inauguration of President Trump.

“If they do that, they have to pay the seventh day,” Bilger said.