Staff at General Motors' German division Adam Opel AG want the carmaker to secure the future of Opel plants in Germany before workers discuss any pay concessions, a labour leader said in a magazine interview cited by Reuters.

In particular, the world's biggest automaker must pick the Opel plant in Ruesselsheim - not a Saab factory in Trollhattan, Sweden - as the site to make its next-generation mid-sized car, Opel works council head Klaus Franz reportedly told Auto Motor und Sport.

"That is a must. We will negotiate this right after Christmas," Franz reportedly said in the interview that was released on Monday ahead of publication on Wednesday.

"The next generation of mid-sized cars that starts from 2007 must be built in Ruesselsheim. Second, global responsibility for developing the next Astra (compact car) has to come to Ruesselsheim, or else there will be no contract for the future," he added, according to Reuters.

"Only when that is in place - as well as long-term assurances for (Opel plants in) Bochum and Kaiserslautern - will we discuss what our employees are ready to give."

Reuters noted that Volkswagen and Mercedes have already done deals this year in which German staff made pay concessions in return for job security.

The report added that GM is supposed to decide early next year where to build the successor to the Opel Vectra and Saab 9.3, which will share a platform. The plant that does not get the work will take a severe blow but not necessarily shut down, GM reportedly has said.