Italy’s antitrust authority (Autorità Garante della Concorrenza e del Mercato – AGCM) was investigating claims that airlines had deliberately raised fares on routes linking mainland Italy with Sicily during the Christmas holidays, Reuters reported on Wednesday.

The investigation followed a complaint by consumer group Codacons, which alleged “a specific collusive will” of airlines to raise prices for domestic Italian flights to and from Sicily, the regulator said.

The complaint also involved ITA Airways, the state-owned successor of former flag carrier Alitalia.

Codacons said any deliberate price distortions “would be particularly serious in the context of the current crisis, of difficulties for consumers and households’ declining spending power,” newspaper l’Eco del Sud reported.

Passengers travelling on domestic flights to Sicily over Christmas faced the steepest ticket prices in Italy, Codacons alleged, saying single economy fares from Bologna or Turin to Palermo were at least 300 euros. The same ticket would be around 400 euros from Milan, and up to 500 euros for the one-hour flight from Rome.

Assoutenti, another consumer rights group, found in a separate survey in mid-December that a one-way ticket from Rome to Palermo cost up to 511 euros on December 20th – more than Rome-New York JFK, which cost 459 euros on the same date.

In a statement to Reuters, easyJet denied any wrongdoing.

“easyJet strongly refutes these claims, adheres to relevant laws and regulations and will fully cooperate with the authorities to demonstrate it has always acted lawfully and competitively in the best interests of consumers,” it said.

The other airlines had not responded to requests for comment, Reuters said.

The cost of domestic flights is particularly sensitive in Sicily, as many people from the island move to mainland Italy to work or study and typically return to spend Christmas with family and friends.