EasyJet cabin crew based in Spain are set to go on strike for nine days in July, the USO union said on Tuesday.
The workers are planning to walk out in three phases, just as the summer holiday season gets going, on July 1, 2, 3, 15, 16, 17, 29, 30 and 31.
They are protesting against low wages, Miguel Galan, the general secretary of USO’s easyJet section, told reporters.
The airline's flight attendants in Spain are demanding a 40% increase to their basic salaries, Mr Galan said, according to Sky News.
"The company underestimated the outlook, was more pessimistic and conservative and is not ready for the demand … this generates a domino effect on us," he said.
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The union, which claims to represent 80% of the 450 staff based in Spain, hopes an agreement can be reached to avoid the strike in a meeting with management on Tuesday, Sky News reported.
It comes after the airline announced it would "proactively" cancel flights at Gatwick in response to a cap introduced by the airport.
It has cancelled dozens of daily flights at the West Sussex airport in recent weeks, including some when passengers were already on the plane.
It said it wanted to “build additional resilience” as the aviation sector across Europe is experiencing “operational issues."
These include air traffic control delays, staff shortages in ground handling and at airports, and increased times for identity checks of new recruits.
Heathrow also asked airlines to cut 10% of flights at two terminals on Monday. The move affected around 5,000 passengers at Terminals 2 and 3 on approximately 30 flights.
Images emerged on Friday of a huge pile-up of passengers’ luggage to add to passenger woes with delays and cancelled flights.
Ryanair 'not immune' to airline chaos
The boss of budget carrier Ryanair warned flight delays and cancellations would continue “right throughout the summer” as airports suffered staff shortages.
Michael O’Leary, Ryanair chief executive, said passengers should brace for a “less than satisfactory experience”, with flight delays due to last across the peak season and some airlines cancelling between 5% and 10% of flights.
He told Sky News this was “deeply regrettable”.
He said: “This problem is going to continue particularly at airports like Gatwick and Heathrow right throughout the summer.
“It will be worse at weekends and better during the week.”
He said 99% of Ryanair flights are getting away and that the experience was so far better at its Stansted base than other UK airports, but admitted it will be a “struggle through the summer."
Mr O’Leary blamed the problems on shortages of airport staff across air traffic control, baggage handling and security.
He said that Ryanair was not immune to the issues, with last weekend seeing 25% of its flights delayed by air traffic control issues and a further 15% by airports handling delays.
He said Brexit was compounding the disruption caused as demand ramps up after pandemic restrictions were lifted, with airports unable to hire workers from abroad to fill posts.
He said: “There are hundreds of thousands of jobs in the UK that frankly British workers don’t want to do.
“These problems will not be resolved until we start allowing people in to do the jobs.”