Ryanair says the disruption caused by the air traffic controllers strike in France will be worse today, as the French workers are joined by their Belgian colleagues.
Yesterday the airline cancelled 220 flights, or 13% of its schedule.
Today it says it will be cancelling 15% of its flights, most of which operate to and from France and Spain.
Aer Lingus, meanwhile, is advising passengers to expect significant delays.
It did not cancel flights when the six-day ATC strike got underway yesterday, but there were some long delays. The airline plans to operate a full schedule of flights today, but is warning that flights to Belgium, Spain, Portugal and southern France will be delayed.
Flights to other destinations may be impacted by knock-on delays.