The Ireland-based budget airline has been cancelling as many as 50 flights a day due to errors it made in planning pilots’ holidays, affecting more than 700,000 passengers’ travel plans.

The U.K.’s Civil Aviation Authority (CAA) reckons Ryanair has been misleading its passengers about their rights following the cancellations, particularly their rights to be rerouted and to get assistance from the airline, including for expenses, meals, and hotel rooms.

The CAA wrote to Ryanair on Wednesday and, dissatisfied with the airline’s response and the emails it has been sending customers, again on Thursday.

The regulator wants Ryanair to issue a press release, linked to from the top of its website, that explains how it will re-route passengers on other airlines, reimburse passengers who have lost money as a result of the cancellations, and “assist passengers who have chosen an option that was not suitable for them as a result of being misled by Ryanair.”

The deadline for this is the end of the working day on Friday. There are various other things the CAA wants, such as revised emails to customers that give more comprehensive information about their rights and options, but the deadline for that is Monday next week.

If Ryanair, headed up by CEO Michael O’Leary, does not play ball, the CAA said the result may be legal action.

Although the law does not provide a cap for the cost of rerouting passengers, the Guardian reported Friday that it had seen an internal memo in which Ryanair’s call-center staff were told they could only offer passengers flights on other airlines if the cost “does not exceed three times the value of the original Ryanair fare.”

At the time of writing—the end of the British morning—Ryanair had not fulfilled the CAA’s demands. However, a spokesperson told Fortune: “We will comply fully with whatever requirements the CAA ask us to.”

A CAA spokesperson declined to speculate about the potential action that could follow if Ryanair doesn’t do what the authority has demanded.