The AGCM watchdog opened a similar investigation into the low cost airline, which has expanded to become Italy's largest carrier, in September. Ryanair is also in a dispute with the Italian government which is trying to hold down the price of domestic flights to its main islands at peak times.

The AGCM claimed Ryanair did not allow physical or online tour operators to access its offers and discounts on its website on several occasions, the newspaper said, reporting in advance a decision by the regulator that is expected to be published later on Monday.

Ryanair, Europe's largest airline by passenger numbers, will have eight days to reply, with the airline's representatives likely to meet the regulator's members on April 18, Il Messaggero reported. Should its arguments not convince the watchdog, it will have to remove all obstacles posed to agencies, the report added.

Ryanair said in an emailed statement to Reuters that the AGCM had been misled by online travel agencies and had wrongly ignored a January ruling by the Milan Court of Appeal that ruled that the airline's direct online sales policy was reasonable and helped sustain lower fares for Italian passengers.

The airline said that unauthorised online travel agencies continued to scam Italian passengers with hidden mark-ups and inflated prices for Ryanair services.

"The Milan Court also ruled that Ryanair undoubtedly benefits consumers, which clearly disproves this AGCM case," Ryanair's CEO Michael O'Leary added in the statement.

The carrier is looking to build on its market-leading position in Italy if more airport slots become available as a result of a potential tie-up between ITA Airways and Lufthansa, with a particular interest in Rome's Fiumicino hub, it said earlier this year.

(Reporting by Giulia Segreti; Editing by Janane Venkatraman and Ros Russell)