"The process of sanctions for failing to inform passengers has been started," a spokesperson for ENAC said, giving no details.

Ryanair last month announced a wave of flight cancellations caused by a shortage of pilots. It is expected to affect more than 700,000 passengers over the coming months.

Ryanair said in a statement that it "complies fully with all EU261 legislation and is taking all necessary steps to re-accommodate affected customers".

Regulation 261 is the EU law on compensating and assisting passengers in the event of flight cancellations and delays .

Britain's aviation regulator said last week that Ryanair had "capitulated" to pressure to inform passengers hit by flight cancellations of their rights, and would keep pushing the airline to fully compensate them.

(Reporting by Masimiliano DiGiorgio; Writing by Philip Pullella; Editing by Greg Mahlich)