Ryanair has said it has cancelled 20 of its planned 300 flights for Friday 3 August due to a strike by Dublin-based pilots.
The airline says all 3,500 affected customers have already been notified by email/SMS.
It will be the fourth day of industrial action by directly employed Dublin pilots.
Taoiseach Leo Varadkar has expressed concern over the escalation in the Ryanair dispute and its impact on holidaymakers.
Speaking in Rome, he called on airline and the Fórsa union to think of the impact a strike will have on "the people and the customers".
He said: "they are the ones that pay the wages of the pilots and the cabin crew and ultimately pay the dividends of the shareholders and keep the board in office.
"I would ask that they get around the table, come to an agreement and allow things to return to normal".
Meanwhile, there has been a second day of strike action by Ryanair cabin crew in Spain, Portugal and Belgium.
Company management says all 50,000 passengers affected have been given alternative flights or have been refunded.
Additional reporting: Ailbhe Conneely