Aer Lingus says it is cancelling between 10% and 20% of flights during the upcoming work to rule by pilots.
Affected flights will be between Wednesday June 26th and Sunday June 30th.
The dispute centres in a row over pay with pilots looking for a pay rise of 24%.
The work to rule - which begins next Wednesday - means pilots will not work overtime, not accept amendments to published rosters, not log into the Aer Lingus portal or answer phone calls outside of work hours.
In a statement Aer Lingus says it has assessed the impact of the industrial action by the Irish Air Line Pilots' Association (IALPA).
"Its indefinite form is designed to severely disrupt passengers in the peak of the summer season," the company said.
"The impact will cause many flight cancellations - many of which may happen close to the time of travel.
"Therefore, in order to protect as many services as possible from the impact of the industrial action, Aer Lingus has to take the step of cancelling between 10% and 20% of our flights on the first five days of the industrial action.
"These cancellations will be implemented over the course of the next two days."
Options for Aer Lingus customers
Details will be communicated to impacted customers over the next couple of days, the carrier says.
Aer Lingus will be offering a number of options to customers who may be impacted.
People scheduled to travel between June 26th and July 2nd will be given the option to change their flights for free.
They will also be able to cancel their flight and claim a refund or voucher.
"Aer Lingus fully understands the anxiety being experienced by customers given the uncertainty caused by IALPA's industrial action and is giving customers as many options as possible, should they wish to change their plans," the company says.
"IALPA's industrial action will have a wholly unnecessary impact on customers who are travelling in the coming weeks, at what is peak holiday season for families. The nature of this industrial action will cause a significant impact on our flight schedules," it adds.
IALPA pay claim
Earlier this week IALPA President Captain Mark Tighe said Aer Lingus management hasn't given them a meaningful offer.
"We are now at a point where this dispute has escalated to indefinite industrial action by pilots," he said.
"We are in this position because management have failed to provide us with a meaningful offer on pay that accounts for inflation and the sacrifices made by pilots to save Aer Lingus during the pandemic.
"Management keep insisting that pilots must sell their working conditions in exchange for any increase in pay. We are absolutely not prepared to do that, especially when Aer Lingus is making enormous profits.
"Our pay claim is for 24%, which equates to inflation since our last pay rise in 2019. Aer Lingus have increased their profits by 400% to €255 million last year.
"Our pay claim is entirely affordable, and Aer Lingus management need to quickly change position if they want to avoid this dispute escalating," he added.
It comes as bookings at Aer Lingus have plummeted since the action was announced by pilots.
New bookings fell by as much as 30% in just one day with the president of the Irish Travel Agents Association (ITAA) saying business was down 'across the board' from travel agents and the public.
