Dublin City Councillors voted unanimously to oppose the handing over of personal details of council tenants to Irish Water.
It is the first formal backlash against the controversial move by local authorities to hand over tenant information to the utility, since this was revealed by the Irish Independent a fortnight ago.
The city council motion, which was proposed by Sinn Féin, received cross-party support and passed without any debate on the topic last night.
The council will now seek an independent legal opinion on whether or not it was legal for Dublin City Council management to hand over tenants details to Irish Water.
Independent Councillor Gary Gannon said there is huge anger among tenants whose details were handed over.
"It is the view of many councillors and myself included who feel it is a total infringement of people's privacy that these details were released to Irish Water," he said.
Sinn Féin Councillor Daithí Doolan said: "We will be studying legal opinion to see how we can overturn the decision to hand over tenants' details and to undo the damage done by Dublin City Council management."