The European Commission has contacted Ryanair regarding the recent cancellation of flights and says it expects the airline to fully comply with EU obligations.
Europe's Transport Commissioner told the European Parliament that the company needs to give passengers correct information regarding their rights, particularly in relation to re-routing and compensation.
The airline was forced into the cancellations after miscalculating pilot leave, possibly affecting over 400,000 passengers.
Transport Commissioner Violeta Bulc said all of Ryanair's communication channels "need to work properly", allowing passengers to communicate with staff.
She also said full information on the complaint handling process must be available on the Ryanair website.
Ms Bulc acknowledged that Ryanair responded and assured the commission that it would address the issues raised.
She said she would pursue contacts with Ryanair and the Irish Aviation Authority during a visit to Dublin in the coming days.
"We expect all airlines operating in EU to fully respect EU rules," she said.
Ms Bulc said it is the responsibility of the Irish Authorities to oversee Ryanair.
Responding to a debate in the European Parliament on the recent cancellation of flights, she said she was confident that if Irish authorities saw wrongdoing, they would respond accordingly.
She pointed out that there are sanctions for infringements of the regulation laid down by member states under national enforcement bodies.
She said she did not believe there was an infringement on behalf of Irish authorities and that she was confident they would do the work they have to do.
Ismail Ertug who is a Social and Democrats German MEP said there were questions for the Irish Aviation Authority who he said were responsible.
Sinn Féin MEP Matt Carthy said there should be no surprise about Ryanair's "disrespectful treatment" of passengers because he said they treat their workers disrespectfully.
Meanwhile, Fine Gael MEP Deirdre Clune, who is a member of the Parliament's Transport Committee, said it should be made clear that the problem resulted from a rostering management failure and not a safety matter, despite varying reports.