Ryanair is facing enforcement action in the UK over its refusal to compensation passengers for flight disruption during a number of strikes this year.
The UK Civil Aviation Authority (CAA) said it was taking the action after the airline decided to terminate its relationship with an approved body designed to resolve customer complaints.
It comes after the airline was hit by a range of strikes across Europe.
Pilots and crew in Spain, Belgium, Holland, Portugal, Italy, Ireland, Sweden and Germany all held strike actions at different times this year – forcing Ryanair to cancel hundreds of flights a day in the worst cases.
The airline was also hit by air traffic control strikes - mainly in France - that also affected rival airlines.
In a statement the CAA said it launched the enforcement action after Ryanair decided passengers were not due financial compensation and terminated its agreement with approved dispute resolution body AviationADR.
It rejected the airline’s claim that the strikes constituted "extraordinary circumstances" – and said passengers were therefore eligible for compensation under EU rules.
In a statement, Ryanair said that courts in Germany, Spain and Italy have already ruled that strikes are an “extraordinary circumstance and EU261 compensation does not apply."
The airline said it expects the UK CAA and courts "will follow this precedent."
It is relying on a Barcelona court decision in October which it said noted that no compensation was due to customers whose flights were cancelled as a result of an internal strike.
It also said airline Lufthansa was not obliged to pay compensation when its pilots went on strike in the past.
The CAA is no stranger to disputes with Ryanair.
After the airline moved to cancel flights affecting 700,000 passengers because of a pilot rota blunder last year, the watchdog’s then-chief executive said he took "with a pinch of salt" a promise by Ryanair to meet its obligations to customers.