Robin Kiely, Ryanair's head of communications, said: "We will be doing our utmost to arrange alternative flights and/or full refunds".
Punctuality fell below 80% over the last fortnight, with the budget airline also blaming air traffic control delays and strikes, and bad weather.
With the cancelation of around 2 thousand flights over the next six weeks, Ryanair hopes to increase its punctuality to 90 percent of flights leaving on time.
The changes in holiday allocations reflects the airline's move to allocate annual leave during a 9 month transition period before December 31 as it plans to switch holiday year, now April to March, to a calendar year from 1st January 2018 onwards.
Dublin flights affected today include flights to & from Brussels, Amsterdam, Manchester, London Gatwick, Bristol and Barcelona.
It claims less than two per cent of flights will be cancelled, but passengers have expressed their fury over late cancellations.
The airline said its is cancelling 40 to 50 flights every day for the next six weeks, in a bid to improve punctuality.
The airline will offer refunds or alternative flights to those affected by the recent announcement.
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Police found Wallen's truck abandoned in an apartment complex off of Gramercy Place near Columbia Mall last Thursday. They said they let him speak at the press conference because they wanted to hear any inconsistencies with the story.
At least one person has said on social media that their flight next week has been cancelled, but is still showing as scheduled on the airline's website.
Speaking on Newstalk Breakfast this morning, Donal explained: "In terms of this overall scheduling issue with Ryanair, they're shifting to a new roster - so the year for them starts in January instead of April".
Maria Joanna Suquitana said guests heading to her brother's wedding in Italy had their flights cancelled hours before departure.
"Ryanair apologises sincerely for the inconvenience caused to customers by these cancellations".
"Publishing the cancelled flights for the next two days ... why not publish them all?"
"We have messed up in the planning of pilot holidays and we're working hard to fix that", Kenny Jacobs, Ryanair's chief marketing officer, said on Saturday (Sunday NZ time).
Ryanair is advising customers affected to check the email they booked their flights with to see if their services are running.