Italy's competition watchdog slapped a 400,000 euro fine on Irish budget airline Ryanair for falling down on commitments to simplify online ticket sales.

The regulator said the airline failed to provide an overall clear price at the very outset of the online booking procedure.

In the period Dec. 1-Feb. 7, Ryanair introduced at the end of the online booking process a 2 percent processing fee on a series of credit cards, the antitrust body said.

It said ticket prices should be "clearly and fully indicated from the very first contact with the consumer in such a way as to make the final price immediately clear," it said.

Consumer association Codacons said all commissions on online air tickets should be eliminated.

"The commission costs for buying with credit cards are very high and are kept hidden by some airlines until the last moment," Codacons president Carlo Rienzi said in a statement.

The fine follows a similar reprimand by the Netherlands Consumer Authority last month which fined Ryanair 370,000 euros for hidden costs associated with tickets purchased online by Dutch travellers.

Ryanair rejected the accusation.

"Ryanair will appeal the unfounded decision by the Italian competition authority," a spokesman for the airline said.