Volkswagen has asked the IG Metall labour union to join negotiations that it is holding with its works council on cutting costs at its inefficient western German plants, the union told Reuters.

The news agency said the move signals that negotiations could be reaching a stage at which changing terms of the existing labour contract will be discussed - the current contract runs to 2011 and rules out forced layoffs at VW's six western German plants.

IG Metall, with members throughout the company, will discuss VW's request in the weeks ahead, it reportedly said in a statement.

Local union chief Hartmut Meine reiterated to Reuters that IG Metall was ready to start talks but was still awaiting concrete proposals from VW, which has said up to 20,000 jobs at the parts and assembly plants were at risk in the reorganisation.

"We are aware of the company's difficult situation," Meine told the news agency, but he added: "IG Metall is absolutely not available for orgies of sacrifice at the expense of employees."

Reuters noted that VW brand head Wolfgang Bernhard reaffirmed this week when launching a new car that sweeping cost cuts were needed to ensure Volkswagen's long-term competitiveness, and has refused to rule out closing some operations.

He riled the works council by saying 1,200 jobs at the main VW plant in Wolfsburg would go when production of the current Golf Mark IV wagon ends. Its successor will be built alongside the Jetta and New Beetle in Mexico.

Bernhard has said a cost-cutting deal with workers should be in place by the end of the year, a target critics say is too far off, Reuters added.