Europe's largest low-priced carrier has faced a string of strikes since it recognised trade unions for the first time in December, damaging bookings and forcing it to consider cutting short-term growth plans if labour unrest continues.
It had initially cancelled 190 flights ahead of action by cabin crew in Spain, Belgium, Holland, Portugal, Italy and Germany.
Unions claim this is the biggest day of action yet against a series of complaints about conditions by Ryanair workers in a raft of countries.
Ryanair took the decision to cancel almost 100 further flights today after German pilots announced strike action at the last minute.
It has rejected calls by the UK's Civil Aviation Authority to compensate passengers whose flights have been cancelled, claiming they were caused by "competitor airline crew, unions and lobby groups" and were therefore "extraordinary circumstances".
Ryanair said the action was taking place in six of its 37 markets and that most of its 400,000 passengers would not be affected.
They want to be given contracts in the countries where they live, rather than under Irish law which they say inconveniences them and affects their ability to access things such as social security benefits. "I made this very clear to Mr O'Leary today", Thyssen said in a statement after a meeting between Ryanair's combative chief executive Michael O'Leary and European Union officials.
In Portugal, 13 morning flights were cancelled and in the Netherlands, 14 of 22 flights were cancelled.
"If need be, there will be further strikes".
However passengers are being advised to check with the airline if they believe their flight is cancelled.
The Dutch union VNV said it was seeking to take legal action to prevent Ryanair from bringing pilots in from overseas to replace striking Dutch crews. The European Commission said that Ryanair is obliged to follow European laws, de facto supporting the strikers.
On Thursday, the airline said it would base two aircraft in Bordeaux and two more in Marseille, using the airports as a hub to add 27 new routes to its northern summer 2019 schedule.
"Respecting EU law is not something over which workers should have to negotiate, nor is it something which can be done differently from country to country".
Ryanair, which now has 86 bases, aims to fly 200-million passengers per year by 2024, up from a forecast of 139-million in 2018.