Ryanair has cancelled 600 flights on 25 and 26 July due to industrial action by cabin crew workers.
The affected flights are to and from Spain, Portugal and Belgium and amount to 12% of the airline's daily flights across Europe.
In a statement, Ryanair said they contacted affected customers by email and text message this morning notifying them of cancellations.
The airline has said that these customers have been offered alternative flights in the week leading up to the strike and the week after.
Alternatively, customers will be offered a refund of their airfares.
They added that any customers travelling to or from Spain, Belgium or Portugal on these dates who have not received an email or text message should expect their flight to operate as normal.
The Ryanair statement said that up to 100,000 passengers will be affected over the two days.
Meanwhile, a two-hour meeting between Ryanair and representatives of the Irish Airline Pilots' Association, part of the Fórsa union, has ended without agreement.
The talks took place in Terminal 1 at Dublin Airport and were limited to two hours because of management commitments.
Speaking after the meeting, which was also attended by representatives of ICTU, Niall Shanahan of Fórsa said the situation had not changed.
He said the union would be reverting to management in coming days with a view to further talks.
A strike affecting a total of 24 flights and around 4,000 customers will go ahead on Friday with a similar stoppage planned for next Tuesday.
This evening Ryanair stated on Twitter that all customers would be accommodated on flights to Europe this Friday because of the "great work" by the majority of its pilots.
It said that 90% of those affected on flights to and from Britain had already applied for refunds or been given alternative flights by 5pm today.
Before the meeting, Niall Shanahan of Fórsa said there was a "small window of opportunity" for industrial action scheduled for next Tuesday, 24 July, to be cancelled or postponed.
