Opel's largest union is referring all questions concerning any implementation of short-term working in Germany to its Works Council as reports circulate the automaker will imminently reveal details of a change in staffing hours.

The speculation surrounds the Russelsheim and Kaiserslautern plants that could see weekly hours worked drop to around 31, with the German government potentially making up the shortfall, but the IG Metall union is deflecting enquiries back to the Works Council.

"We as a union don't want to answer questions about short work because it is the main issue of the [Opel] Works Council," an IG Metall spokeswoman told just-auto. "We have in our region, three main plants, Russelsheim, Eisenach and Kaiserslautern and every plant has its own contract, it is the main thing for the Works Council.

"We now in plans of the contract and it will be finished in October, so there is no possibility to give some issues of the contract. We want to wait until October."

GM, which recently booked a US$400m Q2 loss in Europe after a US$256m Q1 negative result, has spoken for some time about the need to reduce excess capacity at its European subsidiary, Opel-Vauxhall.

In late June, Opel's supervisory board approved a plan involving deep restructuring and huge investment in the product range of the Opel and Vauxhall brands, as well as a new marketing strategy.

GM said it had reached "competitive operating agreements" with unions in England and Poland.

Opel's Works Council, General Motors and the German Labour Ministry in Berlin, were not immediately available for comment.