Irish Ferries has threatened to take court action against Iarnód Éireann in connection with a protest that has prevented the MV Normandy from docking in Rosslare.
The vessel operates between Rosslare and Cherbourg, but sailings have been cancelled as SIPTU members at the port are refusing to handle the ferry.
The protest was mounted to show solidarity with Irish Ferries workers whom the company wants to replace with cheaper labour from abroad.
Irish Ferries is now threatening to respond to the matter by seeking a court injunction against Iarnód Éireann, which operates Rosslare Port.
Meanwhile, both sides in the Irish Ferries dispute are due to resume talks at the Labour Relations Commission today after last night's deadline for a resolution was extended.
The talks are believed to be deadlocked over a recommendation that Irish Ferries be allowed to re-flag its vessels in return for a commitment to pay its workers the minimum wage.
SIPTU believes the only way to get the company to honour Irish labour law is to force it to remain registered in Ireland.