Three major airlines are facing legal action over alleged breaches of consumer law in their handling of passengers hit by disruption to flights.
Aer Lingus, Jet2 and Wizz Air have not made changes to their policies requested by regulators despite extensive discussions, it is claimed.
The Civil Aviation Authority (CAA) has announced it has launched enforcement action against the carriers and will seek a court order unless they comply.
It comes after the CAA carried out a six-month review of airline policies in relation to supporting passengers during disruption, including their approaches to paying flight delay compensation and providing information to fliers about their rights.
The allegations against the three airlines are that:
:: Jet2 and Wizz Air have failed to satisfy the regulator that they are consistently paying compensation for disruption caused by technical faults, despite a Court of Appeal ruling clarifying that airlines must do so.
:: Jet 2 and Wizz Air are imposing two-year time limits for passengers to take compensation claims to court, despite a Court of Appeal ruling that passengers should have up to six years to take a claim to court.
:: Jet2 and Aer Lingus have failed to give satisfactory evidence that they proactively provide passengers with information about their rights during disruption in line with the requirements set out in European regulation.
Andrew Haines, chief executive of the CAA, said: "Airlines are well aware of the support they must provide when there is disruption and passengers have every right to be disappointed that a small number of airlines are not complying with the Court of Appeal rulings and continue to let people down in this way.
"Since the law was clarified last year, we have been active to ensure airlines are applying consumer law appropriately and I warmly welcome the response of those airlines that have changed their policies as a result of this work.
"Our job is not done until all airlines can demonstrate they are providing care, assistance and compensation as required by law.
"While we have no power to secure redress for individual consumers, we are determined to stand up for passengers and are taking this action to safeguard their rights, making sure all airlines consistently provide their passengers with the support and compensation they are legally entitled to."
A spokeswoman for Jet2 said the claims were "materially inaccurate".
She said: "Jet2.com is paying compensation for disruption caused by technical faults in line with the landmark Huzar ruling and have already confirmed this to the CAA. The compensation is up to 400 euros (£289) per person even though our average fare is £80.
"Airlines are entitled to limit to two years the period in which claims can be made by contractual limitations and these have been upheld by the court on a number of occasions. Jet2.com strictly abides by court decisions and is acting in accordance with the law, not contrary to it.
"No enforcement action has been taken. The CAA is obligated to consult with Jet2.com before considering enforcement action. This process has not started. Given the misapprehensions of the CAA, Jet2.com expects that following the mandatory consultation process the CAA will not wish to take the matter any further. We would have preferred that the CAA had engaged with us properly before issuing this press release."
Wizz Air's spokesman Daniel de Carvalho said: "Wizz Air confirms that, following established practice under English law and English court procedures, an application for stay had been made regarding a case in the English courts while the European Court of Justice is considering a relevant case relating to the extent of airlines' liability to pay compensation claims in certain cases involving technical faults and defects.
"After this lawful application for stay was denied by English courts, Wizz Air decided not to appeal this decision and to re-assess the tens of cases where customers claimed compensation after flight disruptions caused by unforeseeable technical faults.
"The UK CAA is well aware that Wizz Air is re-assessing these cases and has confirmed to the UK CAA itself, some time ago, that it will apply the UK CAA's own list of extraordinary circumstances in the relevant cases.
"Wizz Air further confirms that claims can be raised within two years after the flight disruption, in line with its general conditions of carriage agreed to by customers at the time of booking, an approach which has been upheld by the English courts."
A spokesman for Aer Lingus said: "Aer Lingus' procedures, relating to the provision of information to customers affected by operational disruption, are fully compliant with all the relevant regulations.
"We have provided a number of documents to the CAA in recent months to substantiate this point and we continue to engage with the CAA to address their concerns."