UK-based Ryanair pilots have voted to strike in a row over pay and conditions.
The British Airline Pilots Association (Balpa) has announced two walkouts, one from 22-23 August, while the second strike will be from 2-4 September.
It said pilots did not want to disrupt people's travel plans but felt they had no choice after "decades of Ryanair refusing to deal with unions".
But the airline said the "ill-timed" strikes would endanger pilot jobs.
It comes days after the budget airline warned of job losses following a 21% fall in quarterly profits, due to higher costs for fuel and staff, and reduced ticket prices.
Balpa said its members have many disagreements with the airline, including over pensions, loss of licence insurance, maternity benefits, allowances and pay structure.
"We have had no formal offer from Ryanair and it is imperative that we resolve this dispute urgently to avoid strike action," said Balpa's general secretary Brian Strutton.
"No pilot wants to spoil the public's travel plans but at the moment it seems we have no choice."
The union said 72% of its members at the company had taken part in the ballot with 80% of those supporting strike action.
However, Ryanair said that fewer than 50% of Ryanair's UK pilots were members of Balpa, and of these, just 57% voted in favour of industrial action.
In a letter to Balpa, Ryanair's director of HR strategy and operations Darrell Hughes said senior captains were paid up to £180,000 per annum and, because of this, pilot turnover had fallen to zero "in recent months".
He said: "At this difficult time for UK pilots facing base cuts and closures, Balpa should be working with Ryanair to save UK pilot jobs, not endanger them through ill-timed and ill-judged disruption of our customers' travel plans, just 10 weeks before the threat of a no-deal Brexit. We remain available for talks at your convenience."
On 31 July, Ryanair boss Michael O'Leary warned staff in a video message to prepare for job cuts in the coming weeks, saying the airline has 900 too many pilots and cabin crew members.
He said the two weakest markets were Germany, where Ryanair faced fierce competition on price, and the UK, where there were Brexit uncertainties.
"It's been a challenging summer, we're facing into a very difficult winter," he said in the video, seen by the BBC.
"I'm sorry to advise you that this means we need to cut our aircraft numbers and our staffing, not just for summer 2020 but also in winter 2019.
"This will result in some base cuts, some base closures, and I'm very sorry to say, some job losses this winter for pilots and cabin crew, at the end of our summer schedule in September and October, and also some immediately after Christmas."
Mr O'Leary blamed planned cuts to flights next summer due to the grounding of its Boeing 737 Max fleet.
The 737 Max is grounded worldwide over concerns with its software following two deadly crashes.
Mr O'Leary said it been a big factor in the cuts, having delayed the delivery of some 28 planes and having forced the airline to cut flights and close bases.
Mr O'Leary also blamed the "increasing likelihood of a no-deal Brexit in just 12 weeks' time".
"We're worried this could have quite a damaging effect, particularly on our UK bases and on some of our Irish bases, which are heavily dependent on people travelling between Ireland and the UK," he added.