Will the strikes work?
Thousands of workers in eastern Germany have walked out of steel and engineering firms, calling for a shorter working week.
Workers in the former communist region want their week reduced from 38 to 35 hours, bringing them in line with western Germany.
"Thirteen years after German re-unification, we need further steps to achieve the same working and wage conditions throughout Germany," said Klaus Zwickel, head of the IG Metall union.
But employers and the German government have criticised the timing of the strikes, as Germany teeters on the brink of recession.
The German economy is struggling for the third year in a row and last week the finance minister Hans Eichel admitted a 15bn euro (£10.8bn; $17.7bn) hole in the budget.
But the chancellor Gerhard Schroeder's plans to bolster the economy - including cutting unemployment benefits and pensions - have already angered unions.
"At the moment, I work the equivalent of a month longer than my colleagues in the west," said Heiko Wellner, a worker at VW's car production plant in Zwickau.
"Maybe there'll be more jobs if we all work a bit less."
About 2,500 VW workers joined the call to strike on Monday, wearing red vests and caps with "The time has come" slogan.
Unions said about 11,400 workers joined the protest on Monday, with further action planned until Thursday.
VW exports to the US will be delayed
IG Metall argues that by cutting hours, up to 15,000 more jobs could be created.
But employers have countered that eastern Germany is still a third less productive than the west.
Unemployment in the area stands at nearly 19%, more than twice the level in the West.
"What is fair is whatever helps us move Germany forward," said Michael Rogowski, head of the main German industry federation BDI.
Germany's strikes join a wave of protests across Europe.
French workers have been striking since mid-May at government plans to force employees to work longer to qualify for full pension benefits.
Another huge protest is planned for Tuesday, with French ambulance and truck drivers, dock workers, air traffic controllers, postal and electricity workers all downing tools.
In Austria, railways and postal services were planning to walk out from midnight on Monday to protest at a proposed 10% cut in pension benefits.
"People have to understand that the difficulties caused by a day of strikes are nothing compared to the effects of this pension reform plan," said Fritz Verzetnitsch, president of the Austrian labour unions federation OeGB.