It is the result of a strike by pilots who are due to walk out for 24 hours from 01:00 BST on Thursday.
One begged: "Where can we find exact details on the next week flight plans in and out of Ireland during the strike?"
According to the airline, Ireland to Europe flights will operate as normal, as the majority of Irish pilots fly on Thursdays.
The announcement comes despite the fact that Ryanair and union officials are set to meet for talks on Wednesday.
Passengers who have not received an email or text alerting them to the disruption can safely assume that their flight will depart as normal tomorrow.
Nearly 100 pilots working for Ryanair in Ireland voted to stop work on July 12 for 24 hours, and now Ryanair has announced which flights will be cancelled as a result of the strike.
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In a customer update, it said it could not rule out further disruption this month or next and apologised to Irish customers for "these regrettable disruptions".
It said these were routes on which customers could transfer "readily" to other flights on the day of the strike.
The pilots are represented by the Irish Airline Pilots Association (IALPA), a branch of Fórsa trade union.
Ryanair said it was forced into to cancelling the flights after some the airline's Irish pilots signalled their intent to proceed with strike action on Thursday.
"Fórsa wrote to the company (on Monday) to confirm the pilots" body has proposed and reserved a "neutral" venue in order to allay concerns expressed by Ryanair that a meeting between the parties would risk becoming a "media circus'", it added.
"These coordinated strike threats are created to cause unnecessary disruption to customers and damage Ryanair's low fare model, for the benefit of high fare competitor airlines in Ireland and Germany", it said.