Strikers want shorter hours, like their western counterparts

About 10,000 workers at the company's Munich and Regensburg factories were forced to stay at home because of a shortage of parts from eastern suppliers.

Volkswagen said it would have to halt production on Friday at its Wolfsburg unit unless the strikes eased.

The strikers are demanding a reduction in the working week to 35 hours - the norm in western Germany - from 38 hours.

Lower productivity

The action - called three weeks ago by German union giant IG Metall - involves hundreds of firms which supply parts to the car industry.

Manufacturers say the extra three hours are needed because of lower productivity - and warn that the strike could force them to reconsider investment plans for eastern Germany.

The strikes are particularly worrying since Germany's economy is already in deep trouble, struggling for the third year in a row and facing a potential 15bn euro (�10.8bn; $17.7bn) hole in the budget.

Differences in working practices between Germany's two halves are particularly sensitive, since eastern German workers have often felt they have been treated as second-class citizens since reunification in 1990.

IG Metall is therefore tapping into a rich vein of discontent.

Although unemployment is high across Germany, the problem is dramatically worse in the east.

After years of under-investment while Germany was split in two during the Cold War, factories in the east tend to be less advanced and have poorer infrastructure than in the west, one factor in the lower productivity cited by manufacturers.