SIPTU members working in water services in local authorities across the country will begin a campaign of industrial action on 7 June which may take the form of strike action.
The move could lead to significant disruptions to water supplies.
The dispute relates to the transfer of water services from local authorities to Uisce Éireann.
SIPTU said that the objective of the action is to ensure that workers not transferring to Uisce Éireann but remaining in local authorities will not suffer any loss of earnings.
The union claims that significant amounts of money will be lost by water workers on a weekly basis and that there will be a major impact on their pensions if the matters are not addressed.
"We will be serving notice of industrial action on local authorities across the country," said SIPTU Public Administration and Community Division Organiser, Karan O Loughlin.
"The nature of the action will be decided at the end of this week by our representatives from around the country and may well take the form of a strike," Ms O Loughlin said.
SIPTU said it is seeking to ensure the practical application of what was already agreed between union representatives and Government officials as part of a framework for future delivery of water services.
The Department of Housing, Local Government and Heritage said that water services staff who choose not to voluntarily transfer to Uisce Éireann will remain in the direct employment of their current local authority maintaining their current terms and conditions of employment.
"They may continue to work in water services, under the direction of Uisce Éireann, until 31 December 2026. Local authorities will no longer have any involvement in the direct provision of water services to the public beyond that date," a spokesperson said.
"Further opportunities for staff who do not seek to transfer to Uisce Éireann will be identified during the transition period to 2026, including reassignment, redeployment, upskilling and training programmes," the spokesperson said.
"Under the framework, these workers will suffer no loss of earnings relative to their current water services role after they are reassigned within their local authority," the spokesperson added.
The Department said that local authorities will work with staff who are to be reassigned to local authority roles outside of water services, adding that this is expected to be a relatively low number of the overall water services workforce.
A voluntary redundancy scheme will also be made available to eligible local authority water services staff members.
The department said that a framework document for workers sets out the options that will become available generally and empowers them to decide voluntarily on the option which is best suited to their own individual needs.
