Ryanair has written to the European Commission to complain about what it sees as an "abuse" of public service obligation (PSO) routes in Italy.
The airline said yesterday that it had written to the Commission about the award of a PSO route to Italian state-owned airline Alitalia.
Ryanair claims Alitalia has been awarded the right to fly a PSO route between mainland Italy and Sardinia, even though it did not apply for it.
The Italian authorities applied the PSO designation to the route earlier this year, thus effectively halting Ryanair and Easyjet flights that were already flying to Sardinia.
This decision prompted a European Commission investigation and Ryanair is calling for a "speedy conclusion" to the matter.
The airline claims passengers on the route to Sardinia are being forced to pay fares that are four times higher than those charged a year ago.
It alleges that the Italian authorities have "systematically abused" the public service obligation rules to protect Italian airlines.
"Italian consumers should not be denied choice and forced to pay high-fare Italian airlines," said Peter Sherrard, head of communications at budget carrier Ryanair.
Last week, it emerged that Ryanair had complained to the Commission about Air France, alleging that the airline had abused its dominant position and made us of inappropriate state aid.
That complaint came after Air France said it was unhappy with Ryanair's deal to base two new aircraft at Marseilles in the south of France.