Heidelberg has three plants in the Baden-Wrttemberg state including the worlds-largest print machinery manufacturing plant in Wiesloch, which employs 7,000.

Other Heidelberg plants that could be closed on 13 May include its casting facility at Amstetten, which employs 1,400, and its 500-employee folding equipment plant at Ludwigsburg.

A spokesman for IG Metall in Heidelberg said that he expected the unions 6,000 members at Wiesloch would strike unless a last-minute pay deal could be reached.

"This has been planned for two weeks, so we are waiting on what the employers offer. We are asking for 6.5%, but all the talk at the moment is of around 4%," said the spokesman.

While inflation in Germany has fallen to 1.8%, the union has argued that members deserve more after modest wage agreements were reached two years ago.

A spokesman for Heidelberg said he believed that the strikes would not be averted because negotiations would be interrupted by a German public holiday.

"We dont know how many workers will not come in at the moment. But we have prepared for the strike and are confident that it will not impact on delivery times," said the spokesman.

Story by John Davies