Local authority workers who provide services for Irish Water are balloting for industrial action.
The SIPTU members say it relates to a dispute over an attempt by management to unilaterally cut the numbers of frontline water workers.
The union says the decision to ballot comes after an announcement by Irish Water management that it intends to break a service level agreement, and enforce up to 1,500 job losses among workers.
SIPTU organiser, Brendan O'Brien, said: "The company has not explained who would carry out essential work if these jobs are lost".
"It can only be deduced that the plan is to expand the number of private contractors working for the company which will accelerate the creeping privatisation of this public utility".
"Our members are intent on protecting and developing the public water service which they have provided for decades to the highest standard that funding has allowed" he added.
The ballot is set to be counted on Friday November 20th.