BERLIN (AP) — German train drivers started a five-day strike Tuesday, their longest walkout yet in an increasingly bitter dispute with the country's main railway operator.

Passenger train drivers walked off the job at 2 a.m., joining freight train drivers who already started their strike Monday. The GDL union said the drivers won't return to the job until 9 a.m. Sunday.

Railway operator Deutsche Bahn told the dpa news agency that traffic running on its backup schedule was "stable" but only about one-third of its long-distance trains and two-thirds of its regional trains were running. Some subway systems were also affected, including in Berlin and Hamburg.

GDL wants a 5-percent pay increase and shorter hours but the central sticking point is its demand to negotiate for other staff, including conductors, who are traditionally represented by a larger rival union.

Deutsche Bahn has said if GDL is to negotiate for others, it would have to accept the same pay deals agreed to with the other union. Meantime, Deutsche Bahn has offered a 4.7-percent increase in two phases and a one-off payment, and has suggested taking the dispute to arbitration.