Aer Lingus customers who thought they had bagged a trans-Atlantic bargain on the airline's website have been left disappointed after the company said it would not be honouring the bookings.
Around 100 business class seats to the United States - worth over £1,400 each - were mistakenly sold for just ¤5 (around £4) following a technical error on the Aer Lingus website.
Aer Lingus said the problem was linked to a special offer where customers who bought a premier class seat were to be given a second for free.
"The problem was the free seats actually leaked on to the website," an airline spokesman said.
"These were business class seats which would normally sell for ¤1,775 one-way.
"I think anyone would have known it was a mistake when they made the bookings.
"As soon as we identified the issue we cancelled the bookings, apologised to customers, gave them an opportunity to rebook and here we are."
Around 100 customers who applied for trans-Atlantic business class flights in the normal way found they were offered the seats at a cost of only ¤5, before taxes.
Aer Lingus said money was not deducted from customers' bank accounts and that it has written to customers notifying them of the cancellation.
The airline's reaction has been criticised by Irish consumer groups, including the National Consumer Agency, whose Chief Executive, Ann Fitzgerald, said that Aer Lingus would appear to be in breach of contract in cancelling the bookings.
"Blaming a technical error in their booking system in not good enough," she said.
"Aer Lingus formed a contract with the consumer at the stated fare and cannot simply walk away from their obligations."
It is not known exactly how many Ulster travellers were affected, but the Trading Standards Service of the Department of Enterprise, Trade & Investment said that it had received a complaint on the matter.
It said the complaint would be investigated.