A mass meeting of British Airways workers today rejected the airline's plans to cut costs by axing thousands of jobs and freezing pay.
More than 2,000 employees, including cabin crew, sent a "strong message" that they were not prepared to accept an "assault" on their pay, terms and conditions.
The workers, meeting close to Heathrow Airport, also voiced concern that they could face the sack if they resisted the cuts by measures including industrial action.
The airline set a deadline of 30 June to reach a deal on around 3,500 job cuts, a pay freeze and other changes, but no agreement was made.
Conciliation service Acas will chair a meeting between BA and unions on Wednesday in a fresh attempt to break the deadlock, with union officials warning of the threat of compulsory redundancies among some workers.
At a packed mass meeting today, workers overwhelmingly rejected BA's plans to slash costs and instead backed a union plan which officials said could save between £100 million and £130 million.
Unite said it was prepared to consider a two-year freeze on pay, which it said would save £50 million, as well as reviewing the job of the purser among cabin crews.
The union claimed BA wanted to introduce a new "starter rate" of just £11,000, claiming this would lead to a two-tier workforce at the airline.
Officials added that a number of staff would be prepared to take voluntary redundancy, but unions were strongly opposed to any threat of compulsory job losses.
A Unite spokesman said: "Our members have shown that feelings are running very high. They have sent a very clear message that they don't want us to make any further concessions that would lead to an assault on their terms and conditions."
Unite said unions were not threatening industrial action ahead of the fresh talks on Wednesday.
One union source close to the negotiations told the Press Association: "We believe BA is going through the motions with Acas and have a pre-arranged strategy for conflict.
"They are looking at compulsory redundancies as part of 2,500 job losses among cabin crew. They are also looking to resurrect the hated zero-hours contracts for customer service staff which led to the disastrous breakdown a few years ago."
BA was hit by an unofficial strike in 2003 over terms and conditions, and suffered another bout of action in 2005 in a separate row over catering staff.
Pay cuts were agreed with leaders of BA pilots last month, but talks continued for the past few weeks with unions representing other groups, including cabin crew, baggage handlers and check-in staff.
It is believed there are still huge differences between the company's plea for savings to help it survive and the unions' willingness to agree all the cost savings, including changes to terms and conditions.
If the talks break down without agreement, any dispute could lead to a ballot for industrial action which would threaten disruption during the busy summer period.
Union leaders were angered last month when BA announced that almost 7,000 staff had applied for voluntary pay cuts, including 800 who said they would work unpaid for up to a month.
Of the 40,000-strong workforce, 6,940 employees had volunteered for unpaid leave, part-time working or unpaid work by 24 June, which the company said will save up to £10 million.
Chief executive Willie Walsh, who has already announced that he will work unpaid for the month of July, said it was a "fantastic" response, adding: "I want to thank everyone who has volunteered to help us pull through this difficult period."
Unions accused the airline's managers of bullying staff into signing up, a charge denied by BA.
Officials said staff were pressured by email to accept one of the options or face a meeting with a British Airways manager.
BA made losses of £401 million last year and is reportedly losing up to £3 million a day.