Aviation chiefs have warned some airlines about their "unacceptable treatment of passengers" during the current bad weather.
The Civil Aviation Authority (CAA) has confirmed it has written to "a few airlines", both UK-based and overseas-based, saying they had not met their EU laid-down obligations to customers, including rights such as refunds, meals, hotel accommodation and telephone calls.
The CAA said that it was not naming the airlines concerned and that the matter was "ongoing".
The authority added that some airlines were "clearly making real efforts to look after their passengers in difficult circumstances and we commend them for their efforts".
It went on: "However, others are failing to clearly explain EU denied boarding regulations to passengers, and may even be misleading their customers about their rights.
"The regulations stipulate that during periods of disruption, airlines offer refreshments and, where appropriate, put passengers up in hotels.
"The CAA has today written to a number of airlines, both UK-based and overseas-based, to make clear that their behaviour is unacceptable."
The CAA added that it was repeating its advice that if travellers have had to make their own arrangements for hotels and meals during the disruption, they should keep all their receipts and make a claim for the reimbursement of reasonable expenses from the airline concerned as soon as possible.
CAA chairman Dame Deirdre Hutton said: "The EU has put in place regulations to protect people in situations such as this, which not only guarantees people will be looked after, but requires airlines to let people know what their rights are.
"This has not been happening in all cases and it is important that passengers are not being misled. The fact that some airlines are making real efforts to look after their passengers shows that it can be done and there is no excuse for providing misleading information on what passengers are entitled to."