Last year Norwegian said it had poached more than 140 pilots from Ryanair across Europe, revealing a scramble among low-priced carriers for experienced staff.
Ryanair pilots based in Ireland are staging their fourth one-day stoppage today, in a deepening row about terms and conditions.
It said the offer to meet was now pointless and it would notify another 3,500 Irish passengers of 20 further flight cancellations.
However it faces greater disruption next Friday with Irish pilots joining colleagues in Sweden and Belgium on strike, and Ryanair braced for action in Germany and the Netherlands on the same day.
Ryanair shares were down 0.2% at 12.98 euros by 1455 GMT, near two-year lows and well below the level hit in December, when it shocked the markets by ending 32 years of refusing to recognise unions.
Ryanair's Netherlands-based pilots have also voted for industrial action, with the Dutch Airline Pilots Association saying the airline "needs a "wake up call" and a strike in the Netherlands might be the only solution".
Ryanair's chief people officer, Eddie Wilson, said: "Given the non-engagement by Forsa, and the manipulation of the discussions by certain Aer Lingus pilots to ensure that no meetings take place, that unsuccessful strikes keep repeating, Ryanair now feels the only way to introduce common sense is by way of third party mediation, and is suggesting Mr Kieran Mulvey, formerly of the Labour Commission and Workplace Relations Commission".
In a statement, the SEPLA pilots' union said it filed the lawsuit at Spain's top-level National Court after a year of negotiations with Ryanair to employ its members under Spanish rather than Irish legislation failed to bear fruit.
But employees have long slammed their working conditions.
Ryanair cancelled 24 of around 2,300 daily flights after a second one-day strike by Irish pilots.
The airline had also until recently refused to recognise unions, but is gradually doing so as pressure increases.