Ryanair is going to the High Court in a bid to block strike action by its UK pilots.
An application by the airline for an injunction is to be heard by a judge in London on Wednesday.
The proceedings before Mrs Justice Lambert come just hours before industrial action is due to start by members of the British Airline Pilots Association (Balpa) in a dispute over pay and conditions.
The union said earlier this week that because Ryanair "has wasted time with unnecessary court action, their chance to resolve the dispute involving their pilots has been lost".
It added: "Instead Ryanair is relying on legal technicalities to try to persuade the High Court to block the strike.
"Ryanair is seeking a High Court injunction on Wednesday to stop strike action by UK Ryanair pilots, due to take place on Thursday and Friday this week, with a second round of dates in September."
Balpa general secretary Brian Strutton said: "Ryanair pilots in the UK have a serious dispute with their company which will not be resolved by raising legal technicalities in the High Court.
"Their attempt to block lawful strike action is just another demonstration of the bullying tactics the airline appears to favour.
"It means all the time that could have been used to try to find a resolution will now be spent preparing for the court action.
"It's also worrying to see Ryanair continue to sell tickets for strike days - are they prepared to offer compensation to passengers if they are affected?
"I think they should tell passengers exactly where they stand."
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Ryanair said in a statement on Tuesday: "Balpa, who represent a small number of highly paid UK pilots should not be disrupting the return holiday flights of UK families later this week when Ryanair Captains already earn £180,000 p.a and are now seeking unjustified pay increases of between 65% to 121%."
Members of Balpa voted by four to one to back a campaign of action on a 72% turnout.
As well as the legal move in London, Ryanair has this week sought an order at the High Court in Dublin to prevent around 180 pilots based in Ireland from going on a 48-hour strike from midnight on Thursday.
That application was contested by Forsa, which is the parent union of the Irish Airline Pilots Association (Ialpa), and a judge is expected to give a ruling on Wednesday morning.
Additional reporting by Press Association