Drivers for the D.C. Circulator bus system went on strike Tuesday, citing stalled collective bargaining agreement negotiations and “unfair” labor practices during contract discussions with their employer RATP Dev.

The Circulator, jointly operated by the District Department of Transportation and French transportation company RAPT Dev, acts as a shuttle service with fixed routes and schedules serving predominantly Northwest D.C. neighborhoods and the National Mall. Amalgamated Transit Union Local 689 – the D.C. chapter of the national labor union which represents workers in the transit industry – President Raymond Jackson said in a release that RATP Dev left drivers with “no other option” but to go on strike and alleged RATP Dev committed multiple unfair labor practice violations during the negotiations.

“We encourage commuters to seek other forms of public transportation throughout the city,” Jackson said in the release. “After months of negotiations, it has become clear that RATP Dev has been negotiating in bad faith, committing multiple unfair labor practice violations in the process.”

The Circulator operates six stops north of the Foggy Bottom campus, with four stops on its Georgetown-Union Station line and two stops on its DuPont Circle-Georgetown-Rosslyn line respectively. Only two of several dozen Circulator buses operated Tuesday, according to the Washington Post, leaving some riders stranded.