Thomas Cook Airlines faces the threat of a peak summer strike after cabin crew members of the Unite union voted for industrial action.
About half of union members voted, with 74% backing a walk out in a row over rest breaks.
The airline, which operates more than 30 aircraft from 10 UK airports, insisted that it had contigency plans in place to ensure people would still be able to take holidays in the event of strikes.
Union chiefs are due to hold talks with the airline and conciliation service Acas on Thursday and next Tuesday.
A Unite spokesperson said it was not the union's intention to disrupt holiday plans during half-term, which begins this weekend for most schoolchildren.
For a strike to go ahead, the union would need to give Thomas Cook seven days' notice, and that notice has not been served.
Thomas Cook has reduced its cabin crew's breaks from one 20-minute break every six hours to one 20-minute break every 12 hours worked - the minimum indicated in the Civil Aviation Authority's guidelines.
Unite says crew should have at least two 20-minute breaks every 12 hours.
Unite national officer Oliver Richardson said: “We hope that the company take 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.”
A Thomas Cook Airlines spokesman 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."
He said the airline was "committed" to working with Unite to find a solution to end the dispute.
"Meanwhile, we've put together plans to ensure that our customers will still be able to go on holiday, despite any possible strike action."
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