8,000 workers launched a series of co-ordinated strikes at automobile and electronics companies as it and employers spar over wage increases.
The strikes took place at 17 companies, the union, IG Metall, said in a statement.
Car maker Audi was particularly hard hit, as 4,000 workers walked off the floor of an Audi plant in the southern city of Ingolstadt, the union said. Another 1,000 spots went unfilled after a nightshift ended at an Audi plant in Neckarsulm, to the west.
IG Metall leader Berthold Huber said the union could call its members across the country on Monday to mount a series of short-term strikes, "like the country has seldom experienced" if its demands for an 8% pay increase are not met. On Friday the union's branch in the southern state of Bavaria rejected a 2.9% wage increase over the next 12 months.
Employers argued that the credit crunch and financial meltdown makes a better offer unrealistic. IG Metall said its requested wage hike is justified because companies' profits increased 220% between 2004-2007 - a time when wages effectively increased by only 8.7%.
"We are not responsible for the crisis on the financial markets and we're also not ready to take the blame for the gamblers and financial jugglers," said IG Metall chief negotiator Harmut Meine.
If no pay deal is reached, "the real wave of strikes" would start Monday, union chief Berthold Huber said.