Irish Ferries has been ordered to pay compensation to passengers whose travel plans were impacted by the cancellation last summer of planned sailings on its new WB Yeats vessel.
Last April, the company announced that the ferry's arrival on the Dublin to Cherbourg route was postponed after its delivery from the shipyard where it was being built was delayed.
The issue led to the cancellation of planned sailings during July.
Then in June Irish Ferries told passengers that "due to extraordinary circumstances beyond its control" the delivery of the ship had been further delayed.
This led to the cancellation of all planned sailings between Ireland and France involving the vessel for the summer.
The decision forced many holidaymakers to seek alternative means of transport to the continent and also led many others to cancel their trips completely.
Under EU rules ferry companies, like airlines, must in the event of delay or cancellation offer discommoded passengers either free re-routing to their final destination or a refund.
The National Transport Authority (NTA), which is the enforcement body for the rights of sea passengers here, received a number of contacts from those caught up in the situation.
It launched an investigation into the matter to examine whether Irish Ferries had complied with its obligations.
The authority found that the ferry company had not acted as it should have under the relevant regulations.
The NTA was not satisfied that the unavailability of the ferry was an extraordinary circumstance which could not have been avoided, even if all reasonable measures had been taken.
It ordered it to pay compensation to impacted passengers who had already requested it for the delay in arrival at their final destination
It also ordered the company to compensate those passengers who had to travel to use their ports of Rosslare and Roscoff rather than Dublin and Cherbourg as they had originally intended for the extra costs they incurred in rerouting their journeys.
Irish Ferries submitted arguments in response to the ruling which were reviewed and discussed by the NTA's board.
However, at its meeting on Friday, the board decided to confirm the original decision.
Irish Ferries has two months to pay the compensation.
The company said it was disappointed with the NTA's decision and would appeal it in the courts, including the European Court of Justice if needed.
It said the sailing cancellations were due to extraordinary circumstances which were completely outside of the company's control.
"Since the delay was due to unforeseen delays by the shipbuilder FSG, and was notified to passengers months ahead of planned sailings, Irish Ferries does not agree that the company infringed the relevant EU Regulation," it said in a statement.
"In dealing with its customers Irish Ferries believes it took every reasonable action to provide passengers with alternative travel options, from a no-quibble immediate refund to allow them to make alternative travel plans, as well as alternative sailings on the Oscar Wilde out of Rosslare Europort and Land bridge alternatives via the UK. "
The company also reiterated its apology to passengers and said it had given a goodwill gesture of €150 discount for a sailing to France this year to all customers impacted by the cancellations.
It added that ongoing discussions with the NTA around the EU regulation had been a critical factor in its decision last year that it was unlikely to be able to run the Oscar Wilde ferry from Rosslare to France.
It said the NTA's approach to the regulation has contributed to making the route commercially unviable into the future.