The president of the country's largest union, Siptu, has said that the growing use of labour agencies by employers as a substitute for directly recruiting staff posed a grave threat to the living standards of workers.
Speaking at the launch of a campaign for legislation to provide equality of treatment for agency workers, Jack O'Connor again signalled that he did not see how a new national agreement could be negotiated if this issue was not addressed.
"We cannot overstate the importance of this issue. Every syllable of employment protection legislation ever enacted in this country is being circumvented and rendered useless by unscrupulous employers who see the use of labour agencies as the most effective means of exploitation since the abolition of the slave trade 200 years ago."
Siptu has argued that Ireland is one of only three EU countries in which temporary workers recruited through agencies can be employed on lesser terms and conditions to those directly employed.
The union said that between 2002 and 2003 there was a 68 per cent increase in temporary agency work placements in Ireland. It said in the first quarter of 2005 the Central Statistics Office estimated that there were 27,000 temporary agency workers employed here - about 2 per cent of the total workforce.
Mr O'Connor said a new underclass of people was being created who had absolutely no rights in the workplace.
Agency workers had no contract of employment with their beneficial employer, on which all employment legislation turned.
He said Ireland was one of four countries that were blocking the adoption of an EU directive in this area.
"Very soon the Government will have to decide between whatever benefits it believes are being derived from the exploitation of vulnerable people and the continuation of social partnership.
"Because it may well be that they can have one or the other but they cannot have both."
The launch of the Siptu campaign included a number of current and former agency workers who gave details of their experiences.
Conor O'Gorman said he had been working for a construction agency for three years.
On one site a Polish man was working Saturdays and Sundays, and was not being paid overtime rates as he was entitled to under the national agreement.
"One the same site another Polish worker was asked by his foreman two days before his holidays if he would be willing to work the holidays. He said he could not as he was going back to Poland. He was told that if he went back to Poland not to bother returning to Dublin as he would not have a job anymore."
Meanwhile, Minister for Labour Affairs Billy Kelleher is warning shops, bars, restaurants and other businesses employing teenagers in the run-up and during Christmas that they must protect the rights of young workers.
"While many enjoy a very positive experience others may find themselves exploited by unscrupulous employers. It is important, therefore, that young people are aware of their rights, and what steps they can take should they find those being breached."