Aer Lingus has been accused of discriminating against families by its decision to charge passengers up to €15 a flight for pre-booking short-haul flights within Europe.
Labour's consumer affairs spokeswoman, Kathleen Lynch TD, said the new charges imposed significant extra costs on families who wished to ensure they would be seated together on flights.
The new charges also discriminated against customers who did not have access to the internet when booking, she said.
"Aer Lingus has made many claims in recent years about its ability to compete with Ryanair in terms of low fares, but now it appears to have surpassed Michael O'Leary's efforts when it comes to slapping on extra charges.
"Charging up to €15 for the simple privilege of seat selection is unfair and exploitative."
From today until May 22nd, customers booking with Aer Lingus online can pre-book seats on flights in Europe for €3 a flight.
From May 23rd, the cost of prebooking will rise to €10 for the first five seat rows, €15 for an exit row seat, with all remaining seats costing €3 to pre-book.
Ryanair operates free seating on its flights but it does charge €3 a flight for "priority boarding".
Ms Lynch said the concept of low fares was now "close to becoming a joke" as the airlines piled on extra charges for "almost every conceivable item".
Last month, Aer Lingus increased its baggage charges by 25 per cent, only two months after the charges were first introduced.
"The cumulative effect of all these additional charges is that passengers are being misled as to the true costs of their flights."
However, Aer Lingus and other airlines may shortly be forced to display the full price of travel when advertising their fare. Minister for Enterprise and Employment Micheál Martin last month indicated he would introduce new regulations requiring traders to display the inclusive price when advertising.
Ms Lynch supported this approach and called for a more transparent ticket pricing policy by airlines. "All advertisements should be required to detail not just the basic cost but also all extra charges that a passenger will be required to pay."