BERLIN, Germany - Opel labour leader Klaus Franz called on Monday for General Motors to choose a buyer for its European unit this week and vowed to take "spectacular measures" if the U.S. group does not make a decision.

Despite German pressure to back a bid by Magna International, General Motors Co on Friday declined to name the Canadian automotive firm as the winning bidder for Opel, leaving the fate of the carmaker up in the air.

"We have run out of patience," Franz, Opel's works council chief, told Deutschlandfunk radio.

"We have been calm so far, listened diligently and made comments, but that is over now. If nothing changes from General Motors' side by the end of this week, then we will be active, and there will definitely be spectacular measures from us," he said.

The failure to make a decision on the firm's future drew angry reactions from German politicians at the weekend, while they reaffirmed their support for Magna's bid.

The German government, which is facing a federal election on Sept. 27, has offered financial backing for Magna's bid because it believes it would be the best option to save jobs at Opel, which employs around 25,000 in Germany.

Brussels-based financial investor RHJ International is also bidding for Opel.