The U.K.'s Civil Aviation Authority (CAA) has warned Europe's biggest low-cost airline after a further string of cancelled flights threatened thousands of passenger journeys.
Thursday's warning came a day after Ryanair announced it had now cancelled 18,000 more scheduled flights and suspended 34 routes.
"There are clear laws in place, which are intended to assist passengers in the event of a cancellation, helping minimize both the frustration and inconvenience caused by circumstances completely out of their control," CAA Chief Executive Andrew Hainess said.
"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," he added.
"The CAA has today launched enforcement action against Ryanair for persistently misleading passengers with inaccurate information regarding their rights in respect of its recent cancellations," a CAA statement read.
Ryanair, in a terse statement, said it would comply with the law.
The routes suspended included London Stansted to Edinburgh and Glasgow, Gatwick to Belfast and Newcastle to Faro.
Ryanair earlier cancelled up to 50 flights a day through to the end of October, also affecting 400,000 passengers.
The airline initially blamed a rota mistake, leading to a shortage of available pilots.
