Building sites in Dublin could be hit by a rash of strikes in the next few weeks because of the growing use of casual labour.
SIPTU, which represents general operatives, has written to the Construction Industry Federation (CIF) complaining that commitments given by major contractors last September to reduce the use of agency labour is not being honoured.
The union is threatening industrial action on sites where casual workers are provided by recruitment agencies.
Mr Dermot McLoughlin, a SIPTU branch official, said at least 15,000 building workers were being casually employed through agencies. Far from developing a partnership approach to the problem, many large contractors were increasing the use of agency workers, he claimed.
"We have no difficulty with recruiting agencies provided they recruit people for direct employment, but this is cheap labour," Mr McLoughlin said.
On one major site, where SIPTU recently checked members in benefit for balloting purposes, over 70 out of 110 workers were casuals.
Mr McLoughlin said last week alone he had 17 cases involving casual workers being denied various entitlements, ranging from access to the industry's pension scheme to not being paid the registered employment agreement (REA) rate for the job.
The director general of the CIF, Mr Liam Kelleher, confirmed that the federation had written to SIPTU last September, giving commitments on restricting the use of casual labour. If the union thought there were breaches of the REA these would be investigated, he said. At this stage he had no knowledge of any letter from SIPTU.
As many as 150,000 people may be employed through agencies as casual workers in the economy, according to a recent study by the Workers' Party trade union group. This is almost 10 per cent of the Republic's workforce.
The practice is most prevalent in areas such as construction, catering, retailing and food processing.
The chairman of the WP trade union group, Mr Mick Finnegan, is also an officer of SIPTU's construction branch. He said there should be greater legislative protection for agency workers, many of whom were immigrants with little knowledge of their rights.