On May 2 more than 30,000 workers from Germany's IG Metall labor union joined a strike to call for a 6.5% pay rise, the union said.
The industrial action, which began at the weekend, hit big companies such as automotive parts supplier Bosch, as well as Mercedes and Volkswagen and involved employees across the country.
More workers were also expected to down tools later in the day, IG Metall said. In total 36,000 people have now observed the stoppage.
The wage negotiations in the electrical, engineering and metalworking sectors, which employ more than 3.5 million people in Germany, are the bellwether for other key industrial sectors.
Talks are currently in a third round in Germany, Europe's top economy, which has weathered the eurozone debt crisis better than most of its neighbors.
Last month, after several weeks of negotiations interrupted by warning strikes across the country, the two million people working in Germany's public sector secured a 6.3% pay hike for two years.
Copyright Agence France-Presse, 2012