European Commission regulators have opened a probe into whether an Italian scheme giving financial support to carriers operating at Sardinian airports breaches state aid rules.
It relates to a compensation scheme aimed at boosting air links from the Italian island - particularly during the holiday season - under which Alghero, Cagliari and Olbia airports received payment through loans granted by the financial branch of the Sardinian Region.
The Commission says these airports in turn paid financial contributions to airlines, with Ryanair being the only one mentioned by name. The Irish carrier operates bases at both Alghero and Cagliari.
The Commission says it has opened the in-depth investigation as it has "concerns that such public support may procure the beneficiaries an undue economic advantage that their competitors do not have". It acknowledges Italy's argument that the compensation is intended to remunerate airports for the discharge of public service obligation on routes from the island.
The EU's executive body is now inviting comments from interested parties as part of its probe.
Financial support deals at a number of European airports have come under scrutiny from the Commission in recent months. Last June, it widened the scope of a 2007 state-aid probe into Alghero, focussing on a market support deal with Ryanair.
The Commission says it is "currently reflecting" on revisions to the 2005 guidelines on state aid to airlines and airports - a first public consultation was held in 2011 - and it will publish a draft text for public consultation in the coming months.