British Airways (BA) cabin crew have voted overwhelmingly in favour of strike action in a dispute over sick leave, pay and staffing.
The T&G says there has been a "serious breakdown" in relations
Members of the Transport & General Workers Union backed the industrial action by 96%, a move that threatens serious disruption to BA's services.
The airline's managers and the union are now due to hold talks on Tuesday to try to avert a series of walkouts.
BA said any industrial action would be "completely unnecessary".
"We have arranged to meet T&G officials this week and we very much hope they will enter into meaningful discussion with us on the issues the union has raised," said the airline.
"We have not been seeking to achieve new ways of working by imposition, but by negotiation as in many other areas of our business," the airline's statement added.
"The leaders of the (union's) cabin crew branch have created a worrying time for our customers and our staff."
BA shares fell 1.5% to 542.5 pence on news of the ballot's outcome.
T&G Deputy General Secretary Jack Dromey said the strong vote showed just how serious the situation has become.
"BA cabin crew have voted to say the airline has gone too far," he said at a meeting of the cabin crew.
"BA must rebuild the trust of its cabin crew by negotiating rather than imposing change and by listening to its staff rather than riding roughshod over their concerns."
T&G regional secretary Steve Hart added: "BA's success and reputation is built on the loyal workforce that have stuck by this airline through thick and thin.
"Yet while profits and share prices rocket, cabin crew have seen their terms and conditions attacked, an imposition from management rather than negotiation."
The union said cabin crew workers claimed they were under pressure to turn up for work even if they were unwell.
A separate dispute focuses on pension plans.
As part of a plan to lower BA's £2.1bn deficit, the airline has agreed to make a one-off contribution of £800m into the pension fund in return for changes to benefits.
This is the latest in a series of problems that have hit the airline in recent months.
"It's going to be very difficult for BA as they were hit by delays due to fog and security alerts before Christmas," said Global Insight analyst Mandy Kirby
Last month, BA domestic flights from Heathrow were cancelled for three days due to fog.
As well as delayed flights, there was further bad publicity as a backlog of more than 10,000 bags checked in by BA passengers piled up at the airport.
It came after a terror alert in August had also hit BA flights.
Global Insight said BA would be "disappointed" the vote went against them.
"There will be a very strong push to reach agreement but they may feel they've offered a very strong proposal already," said Ms Kirby.
However, she said the damage to BA's image may be limited.
"Customers will be unhappy but BA recently promised to waive as much of the recently announced air passenger duties as they can, so they should survive this on a wave of customer goodwill."