General Motors' troubled German division Adam Opel division is trying a different way of boosting sales: bosses are urging employees who own rival brands' cars to switch to a new Opel.

"Take your Christmas pay and buy an Opel," is the message senior executives and works council leaders are giving staff who arrive in a competitor's car, an Opel spokesman told Reuters, referring to the special year-end pay-out that workers receive.

"It is not the case that they look askance at colleagues who don't drive an Opel," he reportedly said, but they do point out the sweetened terms that staff get when they lease or buy a car from the business.

Reuters noted that Opel is the biggest part of GM's loss-making European operations, where talks are under way on plans to reduce fixed costs by €500 million ($US652 million) a year.

The news agency said the Opel spokesman declined to comment on a report in German paper Handelsblatt that GM was considering outsourcing around 6,000 jobs as part of the efficiency campaign.

Outsourcing has been suggested previously as a way to streamline operations, especially at GM plants like the one in the German city of Kaiserslautern that makes parts rather than whole cars, Reuters said.

The idea, analysts told the news agency, is to combine the operations with those of independent suppliers who sell to a variety of manufacturers, thus reaping economies of scale.