The Taoiseach has raised doubts about the legality of the redundancy offer made by Irish Ferries to 543 of its workers.
The company plans to replace the employees with cheaper agency staff from eastern Europe.
Mr Ahern described the company's actions as 'sharp practice' and 'unacceptable'.
Meanwhile, the country's top industrial relations body, the National Implementation Body, met representatives of the main unions involved in the controversy.
The deadline for responding to the Irish Ferries' redundancy offer is Sunday, while SIPTU's notice of strike action expires on Tuesday.
SIPTU General President, Jack O'Connor, has welcomed the condemnations by the Taoiseach and the Labour Party leader of Irish Ferries' plans.
