Uber’s ride out of an employee class action just got bumpy.

Facing allegations that it has stiffed drivers on tips and expenses, Uber Technologies Inc.’s attorneys at Morgan, Lewis & Bockius had tried to knock out the suit. But on Thursday, U.S. District Judge Edward Chen of the Northern District of California gave plaintiffs the green light, upholding almost all the drivers’ claims and allowing the case to move forward, possibly even as a national class action.