A deadlocked row over job cuts and pay at British Airways could be resolved through arbitration in a move to head off the threat of industrial action.
Talks aimed at agreeing a series of cost-cutting measures including a pay freeze and more than 3,500 job losses ended without agreement on Tuesday night even though the airline had set a deadline for reaching a deal.
The GMB and Unite unions said they would return for more negotiations but it was unclear whether BA would take part.
The company said that the talks had now ended, adding that it would comment "in due course".
Sources close to the negotiations said that the conciliation service Acas or another third party could now be called in to help reach a deal.
A breakdown in the negotiations would lead to the threat of industrial action by thousands of BA workers over the busy summer months, which would heap more problems on BA.
Unions have said they are willing to continue talking to the management about ways of cutting costs and saving money as the airline continues to be hit by the recession.
But a number of sticking points remain, including fears of compulsory job losses as well as concern over planned changes to consultations over redundancies.
The unions said they had never agreed to a deadline and have organised a lobby of workers when they arrive at a hotel near Heathrow Airport in readiness for any fresh talks.
