The CAA say they are also investigating the airline's rerouting policy
The Civil Aviation Authority (CAA) in Britain says it has launched enforcement action against Ryanair in relation to its latest round of flight cancellations.
Ryanair announced earlier it is extending its flight cancellation plan until mid-March next year.
The cancelled flights between November and March could affect up to 400,000 passengers.
The CAA claims the carrier has persistently misled passengers "with inaccurate information" regarding their rights.
Earlier this month, following Ryanair's decision to cancel thousands of flights, the UK CAA wrote to the airline to clarify their legal obligations.
The CAA says they also sought assurances around how and when they would reroute passengers onto alternative flights.
It told the airline to make a "corrective public statement, to ensure customers were not misled and had accurate comprehensive information relating to their rights and entitlements."
But the CAA says in announcing thousands more cancellations on Tuesday "the airline has again failed to provide customers with the necessary and accurate information relating to their passenger rights, particularly around rerouting and care and assistance entitlements, which includes expenses."
"We have now told Ryanair that we are expediting enforcement action against them", it adds.
Separately, it is investigating the airline's rerouting policy.
The UK CAA's chief executive, Andrew Haines, said: "There are clear laws in place, which are intended to assist passengers in the event of a cancellation, helping minimise both the frustration and inconvenience caused by circumstances completely out of their control.
"We have made this crystal clear to Ryanair, who are well aware of their legal obligations, which includes how and when they should reroute passengers, along with the level of information it provides its passengers.
"The information Ryanair published today again fails to makes this clear.
"In expediting our enforcement action we are seeking to ensure that Ryanair's customers will receive the correct and necessary information, to make an informed choice about an alternative flight."
In response, Ryanair says: "We are in correspondence with the CAA and have addressed their concerns".