Irish Ferries has been ordered to pay compensation to passengers who were due to travel on its cancelled services last summer.
There was a delay to the delivery of the new WB Yeats ship which led the cancellation of sailings from Dublin to Cherbourg in France.
The regulatory body - the National Transport Authority (NTA) did not accept that the unavailability of the ferry was due to "extraordinary circumstances".
Thousands of people had to cancel or make alternative plans due to the delay.
Irish Ferries has expressed its disappointment following the decision by the NTA.
"These cancellations were due to extraordinary circumstances which were completely outside of the company’s control," the statement said.
"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 that a goodwill gesture of €150 discount for a sailing to France this year has already been provided to all customers impacted by the cancellations.
Irish Ferries said that "ongoing discussions with the NTA on the interpretation of EU regulation has been a critical factor in regretfully concluding that we are unlikely to operate the Oscar Wilde to France out of Rosslare in 2019".
It added: "The NTA’s approach to the Regulation has contributed to making the route commercially unviable into the future."