Spanish pilots' union SEPLA has filed a lawsuit against Ryanair in a bid to get the airline to apply Spanish labor law to its members' contracts.
Forsa said in a statement: "Ryanair's announcement that it will accept independent third-party assistance in its dispute with pilots, which was made without preconditions, is an unexpected and positive development".
Ryanair pilots based in Belgium have been called out to strike on the 10th of August, the Christian trade union, CNE, and the Belgian Cockpit Association, BeCA, announced on Wednesday.
The airline has said it also expects to face industrial action in Germany and the Netherlands on the same day.
Europe's largest airline by passenger numbers proposed on Friday that a third-party mediator step into talks with a trade union representing its Irish pilots who went on strike for a fourth time before wider stoppages planned around Europe next week.
Cabin crew in Italy, Spain, Portugal and Belgium staged a two-day strike that forced Ryanair to cancel the flights of more than 50,000 customers, the airline's biggest-ever strike.
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Irish has told over 300 pilots and cabin crew that they may lose their jobs as it cuts its Dublin-based fleet by 20 per cent for the winter season after recent strikes hurt bookings and airfares in its home market.
The budget airline's pilots in Germany and Holland have also overwhelmingly backed industrial action, but are yet to confirm any dates for walkouts.
Ryanair said in the statement that it was this tiny handful of Aer Lingus pilots who were behind the scenes for inciting the strikes and sabotaging the talks.
It will be the fifth strike by pilots since July 12.
"Forsa again rejected Ryanair's repeated offers to meet to resolve this dispute on Tuesday next", it said.
The first strike was followed by two more one-day strikes on July 20 and July 24.