Ryanair has until 5pm on Friday to sort out compensation for hundreds of thousands of travellers hit by mass flight cancellations or face possible action by the UK's aviation regulator.
The Civil Aviation Authority (CAA) instructed the budget airline to tell passengers they are entitled to be re-routed by another carrier and explain how that will work.
Ryanair must also publicly state it will reimburse expenses for affected customers, according to a letter from the CAA.
In addition, the Dublin-based carrier must commit to helping passengers who chose an unsuitable option as a result of being misled.
It comes after the regulator accused the airline of "not complying with the law" over its handling of the fiasco.
CAA chief executive Andrew Haines said he was "furious" after Ryanair cancelled an extra 18,000 flights for the winter season on Wednesday - a move that will hit 400,000 customers.
"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 internal memo allegedly instructed call centre staff to offer flights with other carriers - provided the price "does not exceed three times the value of the original Ryanair fare".
The document, unearthed by ITV News, was criticised by consumer group Which?.
Managing director Alex Neill said: "Ryanair appears to be plucking figures out of thin air as there is no legal basis for the arbitrary figure they've set.
"The law says passengers must be rerouted and there's no specified limit on cost. This yet again highlights the importance of the action which the Civil Aviation Authority has started.
"It must force Ryanair to immediately change its behaviour and comply with the law."
A Ryanair spokesman said: "We will be meeting with the CAA and will comply fully with whatever requirements they ask us to."
The latest round of cancellations includes several popular routes used by British travellers, such as 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 after cancelling up to 50 flights a day earlier this month.
Ryanair says the cancellations were brought about because of an error with pilot holiday rosters.
Passengers have expressed their frustration with the airline, with many left out of pocket due to a lack of alternative flights and accommodation bookings they can no longer use.
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 (Michael O'Leary) 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.
"We are furious they are not complying with the law and they are not giving customers what they are entitled to."
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.
It enforces consumer rights for passengers on UK flights under the Enterprise Act, meaning it could take Ryanair to court, where it would face being fined.
However, 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.
The airline said the latest reduction in its schedule will ''eliminate all risk of further flight cancellations".
A spokesman for Ryanair said: “Ryanair responded to the Which? and CAA comments with surprise as EU Reg 261/2004 requires customers to be offered ‘reasonable re-routing’ or ‘re-routing under comparable transport conditions’.
"Ryanair tries to accommodate such reasonable rerouting requests using a guideline (only) of three-times the original airfare.
"This compares favourably with Easyjet’s stated policy, which limits the cost of 'alternative transport' to be 'within the price range you paid for your original return flight or as close as possible'.
"British Airways’ stated policy says only that its disrupted customers will be booked “onto another British Airways flight” with no reference to alternative transport."
"Ryanair respectfully calls on the CAA to explain what enforcement action it took against British Airways when it suffered a computer systems meltdown at Heathrow on the May Bank Holiday weekend earlier this year.”
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules hereLast Updated:
Report this comment Cancel