"It is irresponsible of GM to move at the same time in two different directions -- both toward a sale and a wind-down," IF Metall chairman Stefan Lofven said in a statement.
GM has been trying to sell Saab for more than a year and is preparing to shut the money-losing brand if it doesn't consider the bids for the the 60-year old company suitable.
In a statement on Friday, GM named consultancy AlixPartners -- already closely involved in GM's restructuring -- to run Saab's liquidation. GM said the process is expected to take several months.
GM also confirmed that it had received several offers for Saab and said it is evaluating the bids. This evaluation is not affected by the appointment of AlixPartners, GM said.
Saab an 'amazing brand'
Dutch luxury carmaker Spyker Cars NV made an improved bid for Saab, while Ecclestone joined forces with Luxembourg-based private investment company Genii Capital to pitch a rival proposal. A group of Swedish investors also scrambled to submit a bid.
Genii Capital, which recently invested in Renault's Formula One team, said it will "aggressively work towards a successful closing of the transaction with all the relevant stakeholders of the company."
Lars Carlstrom, a Swedish investor who is coordinating the Genii-Ecclestone bid, said the Formula One boss and his partners were keen on buying Saab mainly for the value of its brand.
"What Genii and Ecclestone have found is that Saab is an amazing brand, comparable to brands such as Porsche and BMW," he said. "They love brands and they really value Saab's brand ... They are really supportive and will definitely be able to bring Saab to new heights."
Ecclestone has $2.4 billion fortune
Ecclestone, 79, is one of the wealthiest figures in sport and was ranked 24th in Britain in the 2009 Sunday Times rich list with an estimated fortune of 1.5 billion pounds ($2.4 billion). He has been a leading player in Formula One since he bought the now-defunct Brabham team in 1972.
Spyker is hoping to gain Saab's technical resources and its distribution network, while bringing its entrepreneurial skills to the new group.
Swedish media reports on Friday named Jan Nygren, an ex executive of the aerospace arm of Saab and former senior official in the defense ministry, as the head of one group of Swedish investors submitting a last-minute bid.
Saab spokesman Eric Geers said any decision over its future and the latest round of bids was in the hands of General Motors. "We all hope these bids are strong enough for General Motors to consider them."
