Chief Executive Michael O'Leary blamed the "mismanagement of EU air travel" for the decision.
Ryanair has said it will close its bases in Cork and Shannon this winter.
The airline also said it is cutting its winter capacity to 40% of what it was last year.
Ryanair said it is also closing its Toulouse base for the winter, as well as making cuts to its bases in Belgium, Germany, Spain, Portugal and Vienna.
As a result of the cuts, the airline said it would be introducing more unpaid leave and job sharing at its winter bases where they have already agreed reduced working time and pay.
There will also be redundancies at the closing cabin crew bases.
Chief Executive Michael O'Leary said while he "deeply regret" the cuts, they had been "forced upon us" by mismanagement of EU air travel during the ongoing global pandemic.
“While we deeply regret these winter schedule cuts, they have been forced upon us by Government mismanagement of EU air travel. Our focus continues to be on maintaining as large a schedule as we can sensibly operate to keep our aircraft, our pilots and our cabin crew current and employed while minimising job losses,” O’Leary said.
“It is inevitable, given the scale of these cutbacks, that we will be implementing more unpaid leave, and job sharing this winter in those bases where we have agreed reduced working time and pay, but this is a better short-term outcome than mass job losses.
“There will regrettably be more redundancies at those small number of cabin crew bases, where we have still not secured agreement on working time and pay cuts, which is the only alternative.”
The airline said it expects to maintain up to 65% of its winter route network, but there will be a reduced number of flights.
The news will come as a blow to Cork and Shannon on the back of the warning from Ryanair last month that the move was being considered.
