Some 10,000 holidaymakers face having their summer ferry sailing plans cancelled as the delivery of a new vessel has been delayed.
The new ship being built in a German shipyard is not likely to be ready for delivery to Irish Ferries in time to honour bookings for sailings in July.
The vessel, the WB Yeats, will not be available to take passengers and vehicles on sailings booked between July 12 and July 29.
All booked sailings between those dates have now been cancelled by Irish Ferries.
Holidaymaker Terry McCorry, from Co Down told RTE's Morning Ireland that his holiday to France has been disrupted due to the delay.
"I booked well in advance because I have some mobility issues and I always like to book a certain cabin. I booked my sailing before Christmas and the whole holiday was put into disarray on Friday evening when I received an email to say my sailing had been cancelled but I would try to be facilitated on another sailing on another boat.
"It left me very unsettled not knowing, having paid a deposit for the holiday home, not knowing if we're going to get on holidays or not. To email late on a Friday evening with very few staff available on the Saturday morning to deal with phonecalls was abysmal... I was on the phone for hours.
"Irish Ferries were able to give me a sailing from Rosslare instead of Dublin 24 hours later so we're missing one night of our holiday. They gave us a cabin that suits my mobility needs and they assured me that the new ship will be ready for when I return later in August."
In a statement, the company said it had been in contact with people whose bookings have been affected.
A spokesman for Irish Ferries said the delayed delivery of the ship was a setback for the company but it was hoped a large number of the affected passengers would be accommodated on sailings from Rosslare aboard the Oscar Wilde.
The company has 'blocked off' space on the Oscar Wilde for affected passengers.
If spaces are not available then Irish Ferries will offer a full refund.
Passengers affected by the cancellations were contacted by email on Friday and offered a €150 voucher as a goodwill gesture from Irish Ferries for use on future sailings. The company said the eventual delivery date of the completed ship had not yet been fully confirmed.
Irish Ferries decided to cancel all those July dates in recent days "in the interests of minimising the level of potential disruption to our customers," said a spokesman.
In the official statement, the company's managing director, Andrew Sheen, said: "We have just been informed by the German shipyard building the WB Yeats that her delivery to Irish Ferries is likely to be delayed.
"We are currently in contact with affected customers and offering spaces that we have held on the MV Oscar Wilde that are close to their booked sailing date.
"In the absence of an acceptable alternative, customers will, of course, be entitled to a full refund."
Sailing times that affected passengers choose to be rerouted on might be a day earlier or a day later than intended as there was no exact overlap between the scheduled departures of the WB Yeats and the Oscar Wilde.
The new €147m ferry was due to start servicing routes from Ireland to France and the UK in July.
It will be the biggest vessel to shuttle passengers to and from Irish ports.