Ryanair pilots across Europe staged a co-ordinated 24-hour strike on Friday to push their demands for better pay and conditions, plunging tens of thousands of passengers into transport chaos at the peak of the busy summer season.
The Irish no-frills airline was forced to scrap some 400 out of 2,400 scheduled European flights as pilots in Ireland, Germany, Belgium, Sweden and the Netherlands walked off the job.
Around 55,000 passengers are affected by the strikes, said Ryanair, which has offered customers refunds or the option of rebooking their journeys.
Ryanair has slammed the stoppages as "unnecessary" but pilots counter that the carrier has refused to engage in meaningful dialogue about collective labour agreements since it began recognising unions in December 2017.
Germany is worst hit by the industrial action, with 250 flights scrapped at 10 airports.
The country's powerful Cockpit union said it had called on Ryanair's roughly 480 Germany-based pilots to walk out from 03:01 am until 02:59 am Saturday.
"There needs to be a rethink at the Dublin company headquarters on how employees are treated," said Ingolf Schumacher, who heads Cockpit's salary policy division.
"Ryanair said there is not one extra cent for personnel costs," he added. "Therefore, no improvement is possible."
In Belgium, around two dozen pilots protested at Charleroi airport, wearing mock badges with slogans like "Ryanair must change" or "Respect us".
In the Netherlands, Ryanair lost a bid to obtain an urgent court order to try to prevent Dutch pilots from joining the industrial action, but the airline said flights to and from the country would not be cancelled.
Belgian passenger Stephane Levens, who had to cancel several business meetings after her return flight from Italy was scrapped, was sanguine about the disruption.
"You know what to expect when you're a Ryanair customer, they're the cheapest," she told Belgian broadcaster RTBF.
Belgian consumer protection group Test Achats meanwhile announced it was taking Ryanair to the European Court of Justice to demand compensation for affected passengers.
The organisation rubbished Ryanair's claim that the strikes were a case of force majeure, and said under EU legislation passengers were entitled to between 250 and 600 euros ($285-$690) in compensation payouts.
The unprecedented cross-border strike action is the biggest escalation yet in Ryanair's long-simmering dispute with cockpit and cabin crews.
The airline already suffered a round of strikes by cockpit and cabin crew last month that disrupted 600 flights in Belgium, Ireland, Italy, Portugal and Spain, affecting 100,000 travellers.
Ryanair, which carries some 130 million passengers annually, averted widespread Christmas strikes last year by agreeing to recognise trade unions for the first time in its 33-year history.
Since then, however, it has struggled to reach agreements.
The famously low-budget company boasts lower costs per passenger than its competitors and is eyeing profits of around 1.25bn euros this year.
Ryanair pilots say they earn less than their counterparts at rival airlines.
Unions also want the airline to give contractors the same work conditions as staff employees.
Another key complaint of workers based in countries other than Ireland is the fact that Ryanair employs them under Irish legislation.
Staff claim this creates huge insecurity for them, blocking their access to state benefits in their country.
Threat to move jobs
At a Frankfurt press conference on Wednesday, Ryanair's chief marketing officer Kenny Jacobs said the company had already offered pilots a 20% pay increase this year, and was committed to giving all its pilots in Germany permanent contracts by the end of the year.
But German daily Bild
said Ryanair's starting salary of around 40,000 euros per year was well below what entry-level pilots made at EasyJet.
And Ryanair's maximum basic salary of 110,000 euros -- which can be topped up depending on flying hours -- was half of what Lufthansa's most experienced pilots took home.
Ryanair has repeatedly said it remains open to further talks with pilot representatives.
But its combative chief executive Michael O'Leary has also warned the airline may shift jobs and planes to more profitable areas if the turmoil continues.
It has already threatened to move part of its Dublin fleet to Poland, which could cost 300 jobs, including 100 pilot positions.
Unions have strongly condemned what they see as Ryanair's attempts to play countries off against each other.