SIPTU has confirmed that its members will begin strike action at the Shanganagh Waste Water Treatment Plant in Co Dublin from 6.30am next Tuesday morning.
The union says the action is in response to their employer’s refusal to recognise union representation for workers.
The new €98.5m facility, which was officially opened last February, treats water for domestic and commercial purposes for 248,000 people living in Dublin and Wicklow.
The treatment plant is run by SDD Shanganagh Water Treatment Ltd under the terms of a contract with Dun Laoghaire Rathdown County Council.
A SIPTU spokesman has claimed that one of its members was dismissed by a project manager for organising trade union activity last March.
SDD Shanganagh (Water Treatment) Limited has denied this claim however, saying that the dismissal had “nothing whatsoever to do with trade union activity”.
A spokesman for SDD said: "The Labour Relations Commission has set aside time on Tuesday May 14 for discussions on the issues involved.
"SDD believes that opportunity should be availed of and we would urge others not to take precipitate action.
"However, should such action go ahead it will have no impact on the operation of the plant at Shanganagh which will continue to function as normal.
"The employer of the staff involved have told us and SIPTU that they totally reject the claim, made by SIPTU, that they don’t recognise the right of their workers to be collectively represented by SIPTU.
"They have always recognised SIPTU, have had many negotiations with them over the years and will continue to do so.
"SDD also wants to make clear that the dismissal referred to by SIPTU had nothing whatsoever to do with union activity."
SIPTU sector organiser Pat McCabe said: "The workers are calling for support in this dispute from all trade unions and others concerned with the protection of human rights.
" They are also calling Dun Laoghaire Rathdown County Council to clearly state its expectation that right of workers to engage in collective bargaining should be respected."