LONDON — Irish budget airline Ryanair was under pressure Monday to provide more information to travelers after canceling up to 50 flights a day over the next six weeks because it mismanaged its pilots' holiday schedules.

Ryanair, Europe's biggest airline by passenger numbers, canceled the flights because it had "messed up in the planning of pilot holidays."

The company promised to publish a full list of the canceled flights by Tuesday, but as of Monday there were only details on canceled flights through Wednesday.

Travelers with flights after Wednesday remained in limbo and took to social media to vent their anger.

"How the hell do you know if you can get back. Publish full list now!" Carole Schofield tweeted.

The company offered to refund travelers for their canceled flights, in accordance with EU law, or to allow them to change their flight for free. It also faces paying compensation of 250 euros ($300) per traveler for flights canceled on less than two weeks' notice.

CEO Michael O'Leary said Monday that the cost of compensation will run up to 20 million euros ($24 million).

"Clearly there's a large reputational impact for which again I apologize. We will try to do better in future," he said.

Shares in the airline fell 1.8 percent to 16.77 euros in Dublin in an otherwise higher market.

Analysts said Ryanair's scheduling problems stemmed from having to harmonize Irish rules with European Union rules on how many hours pilots can fly in a certain period of time.

"The impact in terms of adverse publicity and frustration to customers is large," said Loizos Heracleous, professor of strategy at the Warwick Business School. He does not, however, expect it to have a durable financial impact on the company, which is expanding and is adept at controlling costs and finding new sources of revenue.