Thomas Cook cabin crew have voted by 3-1 in favour of a strike in a row over health and safety.
Members of the Unite union backed walkouts by 74% in a turnout of just over half.
The union is in dispute over changes to rest breaks.
A spokesman for Thomas Cook Airlines said: "We're disappointed Unite cabin crew members have taken the decision to vote for strike action.
"The safety of both our people and our customers is our top priority and we rigorously adhere to the rules around crew breaks.
"We're committed to working with Unite to address their concerns and have already met with the conciliation service Acas to try to find a solution.
"Meanwhile, we've put together plans to ensure that our customers will still be able to go on holiday, despite any possible strike action."
BREAKING: Unite cabin crew members working for Thomas Cook Airlines have backed strike action by three-to-one https://t.co/n2kd6B2jbc
-- Unite the union (@unitetheunion) May 25, 2016
Unite national officer Oliver Richardson said: "We hope that the company takes note of this strong vote in favour of action and works with us constructively to resolve the dispute and avoid any potential industrial action.
"We have already had exploratory talks with Thomas Cook at Acas. Over the coming days we will be approaching further Acas talks in a positive manner and trust that Thomas Cook adopts a similar approach to address our members' legitimate concerns."
Unite members work on flights to major tourist destinations from 10 airports across the UK.
Thomas Cook said the 74.4% vote represented about a quarter of its UK cabin crew, which is over 2,000.