BERLIN (AP) — Germany's biggest industrial union has launched a campaign of 24-hour strikes after talks on demands for wage raises and an optional shorter working week broke down.

The IG Metall union called workers out starting with the night shift Tuesday evening at various companies in regions including the industrial heartlands of Baden-Wuerttemberg and North Rhine-Westphalia.

News agency dpa reported that the companies targeted included truck maker MAN, and the union said Wednesday that production at its main plant in Munich came to a standstill at midnight.

Before talks broke down over the weekend, IG Metall had staged smaller walkouts lasting only a few hours to exert pressure on employers.

The union is seeking a 6-percent raise and an optional 28-hour week. It plans to stage strikes until Friday.