Ruesselsheim, Germany - Workers at Opel - the European offshoot of US carmaker General Motors (GM) - are likely to have to wait until next week to hear whether the future of their group has been secured, company officials told the German Press Agency dpa Thursday.

The signing of a deal to sell a majority stake in GM's struggling Opel unit to a Canadian-Russian consortium has been delayed until next week amid ongoing negotiations over the sale with labour unions and the European Commission.

The new bout of uncertainty about Opel's future comes more than a month after GM announced plans to hive off the stake to a consortium led by the Canadian auto parts group Magna International and which includes the Russian bank Sberbank.

As a result, GM decided against an offer for Opel made by Belgium-based private equity investor RHJ International.

The decision on GM's European Opel subsidiary, which includes operations in Germany, Belgium, Poland, Britain and Spain, formed part of a major global restructuring of the Detroit-based auto group. About half of Opel's 50,000-strong workforce is in Germany.

GM and the Magna-led consortium had been expected to sign off last week on the agreement, which has the backing of the German Government.

Berlin has also said it would provide 4.5 billion euros (6.7 billion dollars) in state-backed guarantees to help Magna restructure Opel.

But last week the European Commission raised objections to the sale arguing that the planned German aid could be in breach EU competition rules.

In particular, the commission expressed concern that the financial support promised by Berlin was conditional on the Magna-led consortium acquiring the majority holding in Opel.

But a company official insisted that was not the case, telling dpa there was "no alternative left to us other than Magna."

The sale to the Magna-led consortium has also faced stiff criticism from unions and governments in other countries where Opel has operations.

They argued that their workforces could be disadvantaged by Berlin's financial support for Opel.

However, Spanish Industry Minister Miguel Sebastian said Thursday that Spain's trade unions and the Magna-led consortium had reached a basic agreement guaranteeing the future of a Spanish Opel factory for the next 10 years.

Earlier this week Opel's Spanish employees announced plans to stage four one-day work stoppages to protest the moves by the Magna consortium to cut jobs at Opel in Spain. (dpa)