Around 19,000 people have had their summer sailings to France cancelled due to a delay in the delivery of a new ferry to Irish Ferries, the company has said.
All planned Irish Ferries sailings to France on the WB Yeats vessel this summer have been cancelled.
In a statement, the company said that the cancellations were due to a delay in building the ship by German company Flensburger Schiffbau-Gesellschaft & Co KG.
Work will continue on the vessel for a few weeks due to delays with the electrical system installation in the hull and deck house, and delays with the delivery of components for public areas.
FSG Chief Executive Rüdiger Fuchs said: "All the key functions of our shipyard and our key suppliers are on the ship, and meet daily to ensure direct and efficient communication.
"Our team is fully focused on completing this first of two large passenger ferries which ICG has ordered from FSG."
FSG said that to address some of the delays it had "made additional funds available to pay second level suppliers directly".
The WB Yeats had been due to begin sailings between Ireland and France on 30 July, but it will not enter full service until September.
Irish Ferries said around 6,000 bookings would be affected by the cancellation.
It said it expects to be able to accommodate 90% of customers affected on its Oscar Wilde ferry, which sails from Rosslare to France.
The company said it checked the possibility of chartering an alternative vessel but there is no ship available.
About 2,500 bookings were affected by the earlier cancellation. However, 95% of those chose to switch to the Oscar Wilde.
Irish Ferries also said it was experiencing a high volume of calls, mails and messages following the cancellation.