Pilots at Ryanair are to stage a series of strikes after voting in favour of industrial action in a dispute over pay and conditions.
The strikes will take place in the height of the school summer break with disruption feared for holidaymakers.
Strikes will be held from 00.01am on August 22 until 11.59pm on August 23 and from 00.01am on September 2 until 11.59pm on September 4.
Members of the British Airline Pilots Association (Balpa) voted by 4-1 to back a campaign of action on a 72% turnout.
A union statement said: "Decades of Ryanair refusing to deal with unions has resulted in two things.
"Firstly, a management that apparently doesn't understand how to work with unions, and secondly a company that doesn't have a number of standard agreements that any union would reasonably expect in any workplace.
"That is why our claim includes many issues including pensions; loss of license insurance; maternity benefits; allowances; and a fair, transparent, and consistent pay structure.
"We have made no progress with Ryanair management on any of those areas at all, seemingly because Ryanair management cannot understand how to go about working with us constructively, or how to negotiate. Ryanair has made no offer to Balpa in respect of its pilots."
Brian Strutton, Balpa's general secretary, said: "We have had no formal offer from Ryanair and it is imperative that we resolve this dispute urgently to avoid strike action. No pilot wants to spoil the public's travel plans but at the moment it seems we have no choice."
Balpa members at British Airways have also voted to take industrial action in a separate dispute over pay.
Ryanair issued a statement saying it was "disappointed" about the potential strike action and that BALPA had "no mandate to disrupt our customers' holidays and flights" as not all Ryanair pilots were members.
Talks between the union and the airline will be held on Thursday under the chairmanship of the conciliation service Acas.
