Ryanair pilots are striking in five European countries, forcing the cancellation of a sixth of the firm's flights during the holiday season peak.
Nearly 400 flights have been grounded across Europe, with that figure set to rise sharply with pilots in the Netherlands deciding to join the walkout yesterday.
Today's unprecedented simultaneous strike action by Ryanair pilots is the latest headache in a turbulent summer for Europe's second-largest airline.
About 50,000 passengers are understood to have been told of cancellations on these flights - as reported by AP.
The Irish airline, Europe's largest low-priced carrier, averted widespread strikes before Christmas by agreeing to recognise unions for the first time in its 30-year history. But the figure could rise to 82 flights if routes between the Dutch city of Eindhoven and the Spanish cities of Reus and Valencia are finally canceled, after a court said on Thursday that Dutch pilots may join the walkout.
The hardest hit countries appeared to be Germany and Ireland, where flights between Berlin, Frankfurt, Hamburg and Dublin and airports in Britain were among those shelved.
Ryanair claimed more than 2,000 flights would operate as normal on Friday.
Another key complaint of workers based in countries other than Ireland is the fact that Ryanair employs them under Irish legislation, arguing most of its employees work on Irish planes.
Since the it first recognised unions in December 2017, walkouts have been staged multiple times by Ryanair staff in various countries. This can mean staff based in other European states are unable to gain access to state benefits.
That was because the strikes were hurting bookings, Ryanair said, and although it was too early to assess the impact elsewhere, it added that the action will hit average fares from having to move customers to flights it could otherwise have sold at a high last-minute price.
"Ryanair took every step to minimise the disruption and we notified our customers as early as possible advising them of their free move, refund or reroute options", the carrier said.
"We want to again apologise to customers affected by this unnecessary disruption and we ask the striking unions to continue negotiations instead of calling anymore unjustified strikes".