Ryanair has been told to compensate customers who lost out when flights were cancelled because of strikes.
The High Court said the thousands of people affected by cancellations or delays during strike action by pilots and cabin crew in 2018 should be compensated.
Ryanair had claimed that “extraordinary circumstances” applied, so it did not have to pay.
But the Civil Aviation Authority took legal action over Ryanair’s refusal.
It argued that passengers were entitled to compensation under EU law.
According to the CAA, under EU legislation, passengers were allowed to make an EU261 claim for flights delayed by three hours or more, cancelled flights or when they were denied boarding.
On Thursday, the High Court agreed with the CAA’s interpretation.
The industrial action in 2018 saw disruption across European airports, with some customers forced to cut short holidays or pay for alternative flights to return home.
Paul Smith, director of the CAA, said: “We believed that these passengers were in fact protected by law and that Ryanair could not claim its delayed and cancelled flights were ‘extraordinary circumstances’. The High Court has today agreed with our interpretation of the law.
“We are committed to protecting the rights of air passengers and are determined to ensure all airlines comply with their legal obligations.”
Ryanair does, however, have the right to seek to appeal against the judgment.
The CAA advised that affected customers should wait for further information before pursuing their claims.
Ryanair declined to comment.
Ryanair recently warned it was in the midst of “the most challenging year” in its 35-year history as a result of travel restrictions imposed amid the coronavirus pandemic.
In February, it said it expected annual losses of up to €1bn (£870m) for the year to March 2021, although it expects travel restrictions to be dropped once high risk groups are vaccinated, unleashing “pent-up demand”.
A recent survey by consumer group Which? found that Ryanair and Virgin Atlantic were rated the worst of the UK’s major airlines for fare refunds.
Both airlines were given a customer “satisfaction score” of just 13% when respondents were asked to rate the customer service they received when applying for a refund from their airline.
One-third of respondents who had a flight cancelled by either Ryanair or Virgin Atlantic said they had waited more than three months for their refund.