Ryanair has been told to correct its compensation policy for passengers by Friday afternoon after thousands of its flights were cancelled.
The UK’s Civil Aviation Authority says the airline must stop misleading passengers about the option to be re-routed with another airline.
The regulator has ordered the budget airline to say publicly how it will re-route passengers who require it.
Ryanair must also say how it will reimburse their out-of-pocket expenses.
In addition, the airline must promise to help any of the passengers whose flights have been cancelled in the past two weeks, but who may have chosen an unsuitable option as a result of being misled by Ryanair, the regulator said.
The demands – which must be completed by 17:00 BST on Friday – cover passengers who were due to fly to and from the UK.
The CAA said if the airline did not meet the deadline, it would carry on with the “enforcement action” launched on Wednesday, which could ultimately see the airline taken to court, with the possibility of an unlimited fine.
The airline recently cancelled flights affecting more than 700,000 passengers, from now until next March, in two separate tranches, because it had bungled the reorganisation of its pilots’ leave arrangements.
The CAA has asked Ryanair to change details on its website by the deadline, saying: “There is still no information here about how expenses will be treated where passengers are re-routed to and/or from other airports or where they otherwise incur additional out-of-pocket expenses as a result of the cancellations.”
“Further changes are therefore required to make it clear that any such expenses will be reimbursed by Ryanair”.
Demanding an end to Ryanair’s “ongoing infringements” of the EU rules, the CAA said Ryanair had still failed to supply information requested a week ago on its refund and rerouting policy.
The regulator said it was “especially interested” in how the airline’s call centre staff had been dealing with passengers.
Evidence seen by the BBC suggests that some travellers have been denied their rights.
For instance, in a web chat with Ryanair on Thursday, a passenger called Matthew Rice said: “You are obligated to re-route me as advised in the CAA’s open letter to you and Ryanair’s policy on the cancellations as provided to you.”
The Ryanair call centre employee replied: “No I am not. Is there anything else I can help you with today?”
The airline said it had reminded its call centre staff on Wednesday about its formal policy, which states that passengers can be re-booked on another airline so long as the cost is not more than three times that of the original Ryanair fare.
The regulator has also imposed a further deadline on the airline to rectify the misleading information given to passengers during the past two weeks.
New emails must be sent to them giving “accurate and comprehensive information on their rights and options”.
Ryanair must offer them again the option of a refund or re-routing, including one with another airline, and tell them how to make a claim for expenses.
Travellers who have accepted a refund must be offered a reimbursement of the difference with any higher fare.
And those who have been misled into accepting an unsatisfactory re-routing must be offered the option of changing it.
Passengers in the second group of cancellations, covering November to March, must have the option of being re-routed with another airline highlighted as an alternative Ryanair flight may not be available.
All the new emails must be sent out by 17:00 BST on 4 October, after first being checked and approved by the CAA.