Ryanair is seeking a High Court injunction to stop strike action by their UK pilots.
If the airline is unsuccessful, British Airline Pilots Association members will stage a series of strikes after voting in favour of industrial action in a dispute over pay and conditions.
They will walk out from midnight for 48 hours.
Ryanair has its main UK base at Stansted, although this is just one airport where strike action will take place.
The British Airline Pilots Association (BALPA) said on Monday that because Ryanair has "wasted time with unnecessary court action", its chance to resolve the dispute involving pilots had been lost.
The airline said affected passengers would be notified by email or text and be offered alternative flights or a refund, or be rerouted.