Alitalia is in danger of losing its licence to fly if it fails to present a rescue plan by the end of the day.
Four major Alitalia unions have backed a takeover of the airline's assets by Italian investor group CAI.
Italy's civil aviation authority ENAC has threatened to withdraw the firm's operating licence on Thursday if it fails to submit a new plan.
The unions dropped their objections to CAI's rescue plan for the flag-carrier at a meeting in Rome.
Premier Silvio Berlusconi has summoned the airline's unions to a meeting in Rome to try to revive rescue talks.
Alitalia had been in danger of losing its licence if it had failed to present a rescue plan by the end of the day.
A group of investors withdrew their offer for Alitalia last week after unions rejected the deal.
Any deal must still win the backing of unions representing pilots and flight assistants for Italy's flag-carrier to be salvaged.
Alitalia, which is estimated to be losing more than 2m euros ($2.9m; £1.58m) a day, is currently flying with a provisional licence, according to ENAC.
After weeks of wrangling, the four unions agreed to support the framework deal at a meeting at Italian Premier Silvio Berlusconi's office.
Efforts to save the troubled airline came to an abrupt halt last week.
Italian investor group CAI had offered to take over Alitalia's profitable assets, but it withdrew its offer last week after some Alitalia unions refused to sign off on their plan.
CAI had pledged to inject $1.4bn into the bankrupt airline, sell off unprofitable assets and merge the rest with Italy's second biggest carrier Air One.
But six unions, who were unhappy at plans to cut 3,000 jobs, opposed the move. Three unions had backed the deal.
Earlier this week, the administrator for the airline placed advertisements in four newspapers in a bid to lure buyers for the carrier.
Any possible buyers have to express their interest in the airline by 30 September.
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