Port workers at Dublin and Rosslare have said they will turn away Irish Ferries vessel the MV Normandy if it tries to dock in either port.
Siptu workers at both ports reportedly said this evening they would refuse to handle vessels belonging to Irish Ferries.
The MV Normandy is scheduled to leave France for Rosslare this evening and is due to dock at the port tomorrow.
Earlier, Irish Ferries denied reports that it considered the use of tear gas on crew members. A newspaper report suggested the option was raised at a meeting as one of a range of extreme measures.
Irish Ferries issued a statement this morning rejecting "in the strongest possible terms" the claim made in today's edition of The Irish Independent.
Earlier, trade union representatives belonging to the International Transport Workers' Federation claimed a member of the British seafarers' union, NUMAST, was refused permission to board the Irish Ferries vessel, Ulysses.
The Federation is claiming the crew on the Ulysses are not free to leave the ship.
Trade union representatives last night discussed possible ways of escalating the dispute as managment and crew began a stand-off over company plans to outsource jobs.
Siptu is urging the Irish Congress of Trades Unions to hold rallies across Ireland on Friday to support the ferry crews.
Union boss Jack O'Connor said yesterday: "The Irish Ferries dispute is a defining moment in the relations between employers and workers in this country."
Four ships' officers are continuing to barricade themselves into the control room of the Isle of Inishmore at Pembroke, while crews attached to the Ulysses and the Jonathan Swift are threatening to take similar action if the company tries to sail with cheaper agency staff.
Yesterday the Taoiseach, Mr Ahern criticised the way the company had handled the redundancy dispute.
This is a retrograde step by them, this is not in line with Irish industrial relations, they are trying to turn back the clock, they should still think about it, about everything that they have done in their handling of this. I fundamentally and totally disagree with [it]," he said.
Meanwhile, Ictu is to hold a meeting on Tuesday morning to discuss the ongoing dispute.
The meeting is being arranged following Siptu president Jack O'Connor's call to hold rallies nationwide next Friday, December 2nd, to support Irish Ferries workers.
Mr O'Connor said the dispute represented a defining moment for workers, employers, government and every citizen about the type of society in which they wished to live.