Alitalia said it would appeal a ruling by Italy's antitrust authority that said it, along with its unit AirOne, was running a monopoly on the highly profitable Rome-Milan route and must give up some slots.
The authority, ending a probe that began last year, said the airline must give up slots between Rome Fiumicino and Milan Linate airports by October 28.
It did not specify how many slots it had to relinquish but said that the airline must open itself up to "effective competition" during peak hours in the early morning and late afternoon.
Alitalia said it would appeal the antitrust ruling, and argued that the Rome-Milan high-speed rail link already constituted competition for airlines.
Alitalia chief executive Andrea Ragnetti said he was "surprised" by the ruling.