An estimated 5,000 workers have taken part in a march to the Dáil in protest against controversial redundancy plans by Irish Ferries.
The company wants to make over 500 of its workers redundant and replace them with cheaper agency workers.
The march was backed by leaders of the 15 largest trade unions who voiced their opposition to the proposed EU services directive.
The SIPTU President, Jack O'Connor, has said the directive would undermine pay and conditions by allowing the lowest rates in the EU to apply.
Addressing the rally outside Leinster House, Mr O'Connor said workers should be prepared for more marches during the winter.
Representatives of Labour, Sinn Féin and the Green Party also attended the event.
The General Secretary of the ICTU, David Begg, said trade unionists needed guarantees of higher standards and effective enforcement if they were to enter talks on a new social partnership agreement.
He condemned Irish Ferries for what he described as the exploitation of vulnerable workers from other countries and said the facts did not support the company's contention that competitive pressure had led to the proposed job losses.
Mr Begg warned that the race to the bottom could lead to social tensions and a misjudged antipathy towards foreign workers.
