The airline has warned up to 300 jobs are at risk
Ryanair cabin crew in Spain, Italy, Portugal and Belgium are staging a second day of strike action on Thursday, with the cancellation of hundreds of flights.
Cabin crews in Italy are also staging a one-day strike.
While the union representing Irish-based pilots has confirmed a fourth day of strike action on Friday August 3rd in a row over seniority, base transfers and annual leave.
Fórsa said more action would follow later this month unless the airline's management "changed tack" and "negotiated in good faith" on the issue of base transfers and related matters.
While the airline also warned on Wednesday that up to 300 jobs are at risk, with plans to cut the size of its Dublin fleet.
In a statement, Fórsa said it believed the airline's decision to issue protective notice to 300 of its staff on Wednesday was "an attempt to put pressure on its employees."
It said the "provocative act, which was likely to harden pilots’ resolve, had escalated the dispute while demonstrating management’s unwillingness or inability to negotiate with unions in good faith."
The carrier has approved plans to cut its Dublin-based fleet from 30 to 24 aircraft for the winter season.
It said these reductions have been driven by the "rapid growth of Ryanair's Polish charter airline... allied to a down turn in forward bookings and airfares in Ireland partly as a result of recent rolling strikes by Irish pilots".
It said these strikes have had "a negative effect on (close-in) high fare bookings and forward air fares as consumer confidence in the reliability of our Irish flight schedules has been disturbed."
The carrier said its Polish airline, Ryanair Sun, will now offer over 10 aircraft to Polish tour operators - more than double the five aircraft offered in summer 2018.
"We expect few route closures from Dublin, although some routes may suffer frequency reductions", it said.
In the light of the Dublin base cuts, Ryanair issued letters of 90 days protective notice to over 100 pilots and over 200 cabin crew employees.
It said their services "may not be required" from October 28th onwards, due to this reduction in the winter fleet.
Ryanair said it will now begin consultations on redundancy, which, if redundancies are necessary, will be determined by Ryanair's assessment of flight performance, productivity, attendances, and base transfer requests.