The Taoiseach questioned the legality of a plan by Irish Ferries to replace the 543 Irish staff on its vessels with workers from Eastern Europe when the issue was raise in the Dáil today.
Speaking on the first day of the new Dáil session, Mr Ahern described the company's plan as "sharp practice and totally unacceptable".
He said he had written to the company's chief executive to express his concerns and added that the Government had sought legal advice on the matter.
Labour leader Pat Rabbitte said: "We have very seldom seen anything so blatant as disemploying the entire workforce in order to employ slave labour".
The National Implementation Body (NIB) is meeting this evening to consider the plan.
Earlier the body - which polices implementation of national partnership deals - met with officials from the Seamen's Union of Ireland and Siptu which represent the workers.
It is understood that Irish Ferries management was not invited to the talks but was represented by the employers body IBEC.
The company has already been served with strike notice by Siptu over the redundancy plan.
The redunancy package offers workers up to eight weeks' pay per year of service with no cap. This is likely to prove attractive to a large number of workers, some of whom stand to receive more than €200,000.
But while the Seamen's Union of Ireland accepts many workers may opt to take redundancy, a spokesman said it was "far from a voluntary severance package".
"The company is basically saying take this or get out," he said.