BERLIN (AP) — A union representing German train drivers has called members out on a five-day strike starting Tuesday, its longest walkout yet in an increasingly bitter dispute with the national railway operator.

The GDL union said passenger train drivers will walk off the job at 2 a.m. (0000 GMT) Tuesday and won't return until 9 a.m. (0700GMT) on May 10. Freight train drivers will start their walkout Monday afternoon.

The long-running dispute between GDL and railway operator Deutsche Bahn already has produced a string of strikes. GDL wants a 5 percent pay increase and shorter working hours. But the central sticking point is its demand to negotiate not just for train drivers but for other staff including conductors who are traditionally represented by a larger rival union.

Deutsche Bahn says it can't accept different pay deals for employees who do the same job. It has suggested taking the dispute to arbitration.

Announcing the latest walkout on Sunday, the union accused Deutsche Bahn of "trampling on GDL members' constitutionally protected rights" and playing for time until a new law aimed at curbing disruption by smaller unions comes into force this summer.

Germany long had relatively cordial labor relations, with big unions negotiating wage deals for a whole company's workers, but recent years have seen a rise in the power of small unions representing single or a few professions — such as airline pilots or cabin staff.

Under the new law, when there are several wage contracts for the same group of employees at a company, only the one negotiated by the union with most members would be valid. The legislation is expected to face court challenges.

During previous walkouts, government-owned Deutsche Bahn has kept a limited number of trains running on key routes but there have been widespread cancelations.

Transport Minister Alexander Dobrindt criticized the strike announcement, telling the Bild newspaper that that "the limit of people's acceptance of this dispute is increasingly being reached."