Ryanair has threatened legal action against Italy's civil aviation authority, saying it refused to grant the airline access to a prized domestic slot to protect flag carrier Alitalia.
Ryanair chief executive Michael O'Leary, speaking in Rome, said the company had already sold thousands of seats on the route from Rome to Alghero, located on the Mediterranean island of Sardinia.
"We're going to send an e-mail to the 10,000 people, asking them to write or telephone (the civil aviation authority) and the Italian Transportation Ministry to get an explanation," Mr O'Leary was quoted as saying by Italian news agency ANSA.
ANSA said Mr O'Leary had given Italy five days before he would seek legal action.
The civil aviation authority, known by its Italian initials Enac, sent out a terse statement denying it acted improperly and questioned why Ryanair was selling tickets on a still unauthorised route.
"ENAC ... neither favours or opposes any company or operator in the sector," it said, adding the infrastructure minister had only requested Ryanair simply modify its operating plan.
Among the requested changes reported by Italian media are lower-priced tickets for residents of Sardinia under a "regional continuity" policy applying to some domestic destinations.
"In the specific case of Ryanair, ENAC acted only according to the indications coming from the ministry," it said.
Ryanair has been aggressively expanding domestic service in Italy from its Rome base this year, offering new domestic flights to Venice and Verona.
Alitalia, which is 62 per cent state-owned, is battling to win back domestic market share and pull back from the edge of bankruptcy. Ryanair and other budget airlines have urged the European Union to reject Alitalia's restructuring programme, which is currently under review in Brussels. They accuse Rome of providing illegal state aid to prop up Alitalia.
The restructuring aims to return the loss-making Italian airline to break-even in 2006 and allow for a capital increase of up to €1.2 billion.