Ryanair is breaking the law in its handling of flight cancellations, the boss of Britian's aviation regulator has claimed.
Andrew Haines, chief executive of the Civil Aviation Authority (CAA), said he was "furious" with the Dublin-based carrier because it is not telling passengers they are entitled to be re-routed by other airlines.
"They are not making it clear to people their entitlement," Mr Haines told BBC Radio 4's Today programme.
"If they follow through on what they are saying then they would be breaking the law."
A Ryanair spokesman said: "We will be meeting with the CAA and will comply fully with whatever requirements they ask us to."
On Wednesday the airline cancelled an extra 18,000 flights for the winter season in a move that will hit 400,000 customers.
Ryanair is facing a multi-million compensation bill for cancelled flights after it previously revealed it was shelving up to 50 flights a day up to the end of October.
It says the cancellations were brought about because of an error with pilot holiday rosters.
Mr Haines said airline passengers are "well protected by the law".
He went on: "They are entitled to compensation and if there is a cancellation they are entitled to be re-routed by other airlines.
"The chief executive of Ryanair has gone on record and said he is not going to do that. He then issued a clarification.
"But yesterday when they announced 18,000 further cancellations they failed to follow through on that.
"So we are furious they are not complying with the law and they are not giving customers what they are entitled to."
The CAA is launching enforcement action against Ryanair for failing to give customers accurate information about their rights.
The regulator asked for a meeting with the airline as part of a consultation that will last at least seven days and could take legal action for breaching consumer protection laws.
It says Ryanair has falsely claimed it did not have to re-route passengers on other airlines, particularly when there are no other services available.
The CAA also accused the airline of stopping short of providing details on its obligations to refund additional expenses incurred by passengers as a result of cancellations including for meals, hotels and transfer costs.
Ryanair said on Wednesday it was suspending 34 routes for the winter season, spanning from November to March 2018.
They include several popular routes used by British travellers, including Stansted to Edinburgh and Glasgow, Gatwick to Belfast, Newcastle to Faro, and Glasgow to Las Palmas.
It adds to mounting anger against Ryanair, which was already coming under heavy fire over its initial cancellations earlier this month.
Mr O'Leary has blamed the move on mismanagement of pilots' annual leave, leading to the over-allocation of blocks of holidays.
Ryanair said the latest step will "eliminate all risk of further flight cancellations" and remove the risk of similar problems recurring next year.
The CAA enforces consumer rights for passengers on British flights under the Enterprise Act, meaning it could take Ryanair to court, where it would face being fined.
But it has no powers to stop the airline from operating in the UK on the grounds of how it treats passengers.
Ryanair's operating licence is handled by the Irish Aviation Authority.
