BERLIN (AP)—General Motors Co.’s decision to scrap the sale of European subsidiary Opel raised new uncertainty Wednesday over the unit’s future, astonishing politicians in Germany and Russia, and prompting workers to plan walkouts in protest.

The GM board’s unexpected decision to call off the sale to auto parts maker Magna International Inc. and Russian lender Sberbank was a startling end to months of haggling.

Now German workers worry that GM will make even more cuts to return Opel to profit than Magna would have. Still, the decision won a cautious welcome from union officials in Britain and Poland, where workers had feared possible cutbacks in a Magna takeover.