After weeks of brinkmanship and repeated predictions of its imminent collapse, Alitalia's unions have been given a "final" deadline of tomorrow to accept or reject a rescue offer for the bankrupt airline.

"By Thursday morning we will ask who is on board, and we will sign with whomever agrees," said Maurizio Sacconi, the Labour Minister. He said there was no question of making further amendments to the offer from CAI, the group of Italian investors bidding for the airline.

The investors, led by Roberto Colaninno, chief executive of Piaggio, will decide whether to go ahead with their offer even without support from all nine of the Alitalia unions, Mr Sacconi said.

Forty flights on Italian and European routes were cancelled today because of a strike by CUB, a small union. However, an Alitalia spokesman stressed that the cancellations had nothing to do with rumoured fuel shortages.

Alitalia's four biggest unions have accepted new concessions by CAI, which offered to include 1,000 more workers than in the original plan. However, unions representing the 7,000 pilots and air crews continue to oppose the deal.

Alitalia's bankruptcy commissioner has warned that the airline is running out of cash for fuel and that flights could be grounded if unions do not agree quickly to the CAI buyout offer.

The rescue plan involves 3,250 redundancies and longer hours for the same pay. "This is a massacre," said Fabio Frati, the CUB union leader.

However, Altero Matteoli, the Transport Minister, said it was "absurd and irresponsible" to strike at a time when Alitalia could barely afford to keep flying.

Augusto Fantozzi, the government-appointed special commissioner running Alitalia, said "cash is running out", and the only offer on the table was the CAI bid, although during a visit to France this week Silvio Berlusconi, the Prime Minister, again sought help from Air France. However, he threatened not to extend redundancy benefits to Alitalia workers if the CAI deal was not accepted.

He told reporters in Paris after talks with President Nicolas Sarkozy that the Government's guarantees of 80 per cent pay for up to eight years for 3,250 workers who would be laid off under the reorganisation plan could not be extended to all Alitalia's 20,000 employees.

Air France-KLM has expressed interest, but Mr Berlusconi also pointed to Lufthansa as an "ideal partner." Air France-KLM withdrew from talks in the spring to buy the Government's controlling stake in Alitalia.

Mr Berlusconi, who was then fighting an election campaign, which he won, vowed to find "an Italian solution".

Meanwhile, Greece will close Olympic Airlines, its loss-making flag carrier, and relaunch it as a new company called Pantheon under a plan approved today by the European Commission.

The Greek Government had pledged to find a buyer or restructure the airline by Christmas, after years of unsuccessful attempts to sell.

The Olympic trademark and landing slots will be retained, but the carrier will be cut to 65 per cent of its existing size. About 8,000 employees may lose their jobs.

The European Commission ruled in 1996 that Olympic was in breach of EU state aid rules and told the airline to repay €850 million (£673 million), but the commission has said that no state aid is involved in the restructure plan.

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