Employees belonging to Germany's largest union have begun a series of brief regional stoppages in a growing dispute over pay and productivity.
German workers want to defend existing working conditions
IG Metall staff at a DaimlerChrysler plant in the south-west of the country stopped work for several hours.
More warning strikes, in which staff temporarily down tools to emphasise their demands but do not disrupt production, are expected on Wednesday.
Unions say staff must be given a greater share in firms' profitability.
Making a point
IG Metall, which represents 3.4 million manufacturing workers, has warned that the regional stoppages could be a prelude to sustained national action over pay and working conditions.
It is seeking a 5% rise in wages and guarantees on working hours, including the maintenance of traditional toilet breaks.
The union said that up to 1,000 staff had joined in the action at DaimlerChrysler and similar stoppages would take place across the state of Baden-Wuerttemberg on Wednesday.
Carmaker Porsche and Bosch are expected to be targeted.
"On Ash Wednesday, we will begin with public actions, not just for one day and not just for one company," Joerg Hofmann, the regional head of IG Metall, said.
Employers have said that the wage demand is unsustainable and will result in job losses.
Many German states want to lengthen the working week from 38.5 to 40 hours to boost productivity.