Ryanair's new bag charge policy is being investigated by Italy's competition watchdog over claims it could amount to unfair commercial practice.
Antitrust says hand luggage is an "essential element of transport" that should be included in the ticket price. Not doing so distorts the final price of the ticket and does not allow a true comparison with other airlines, it said.
Ryanair's new policy is to charge €9 (£8) for those who want to take on a 10kg (22lb) bag. Passengers will still be able to take a small personal bag on to the flight but it must fit under the seat in front.
Italian consumer group Association Codacons told the BBC: "If its unfair commercial practice on hand luggage is confirmed, Ryanair... should reimburse all its customers who suffer unfair additional costs.
Ryanair has said the new policy will eliminate boarding and flight delays.
Yesterday Ryanair faced a shareholder revolt at its AGM in which nearly 30 per cent of shareholders voted against the airline's long-serving chairman David Bonderman, saying his lengthy time on the board has prevented him from providing independent advice to chief executive Michael O'Leary.
Ryanair's chief marketing officer Kenny Jacobs said: "We look forward to cooperating with this Italian inquiry. All Ryanair customers are free to bring one piece of carry-on bag onboard. But no airline customer has a right to unlimited carry-on bags. For safety reasons, most short haul aircraft cannot accommodate two carry-on bags for each customer.
"From November, half our customers will continue to bring two free bags onboard and the other half will continue to travel with one free small bag (which has been increased by 40% in size) and can, if they so choose, check-in a second 10kg bag for a new lower fee of €8 (currently Ryanair’s lowest cost check bag is €25).
"All other airlines, including Alitalia, Easyjet and BA, restrict the volume of carry-on bags for safety reasons. We look forward to explaining these safety restrictions and generous carry-on bag policy to the Italian authority.”
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