Ireland's largest trade union has backed protest against the controversial water charges.
Siptu said it will begin talks with other unions about peaceful demonstrations against the new bills which will begin dropping on doormats in the New Year.
The union, which represents 200,000 workers, previously refused to join with Right2Water, an umbrella group backed by five unions.
But responding to the "regressive" billing regime revealed by the government this week, it has vowed to work with the campaign towards an "agreed approach" against the fees.
Jack O'Connor, union president, said many people simply can not afford the latest levy, after six years of hard-hitting austerity measures.
"There are a great many people for whom it is not affordable, and there are a great many people for whom nothing more is affordable," he said.
"There are a great many people at the present time who can not live on what little they have, without charging them any more.
"These people are not being invented, they are out there and they are suffering a great deal."
The union's attack will come as a further set back for the Fine Gael/Labour coalition, which was hoping to quell public dissent with revised, lower charges announced by Environment Minister Alan Kelly on Wednesday.
Taoiseach Enda Kenny was met with hundreds of jeering protesters chanting "we won't pay" as he arrived in Cork this morning amid a heavy Garda presence for a jobs announcement.
Backbench Fine Gael TD Noel Coonan today retracted his remarks in the Dail yesterday, comparing protesters with fundamentalist Islamic State terrorists, known for ethnic cleansing and beheading western journalists.
Mr Coonan, who represents Tipperary North, said anarchists would have been a more appropriate description.
Siptu agreed its opposition to the water charges at a meeting of its ruling national executive.
Warning that the Irish Water model did not offer a long-term solution to the problem, it has called for the utility to be replaced with a "democratically controlled" water authority.
It also urged a referendum to ban any future privatisation of the water supply.
The union has proposed all homes get adequate supplies at no charge, with fines for wastage or overuse only as a conservation measure.
Under the Government's scheme there is no fairness or incentive to save water, said Mr O'Connor.
"Austerity measures are not necessary any more, the economy is growing and we are ahead of targets in terms of emerging from the recession," he added.
Siptu said it will now work with other trade unions and organisations, including Right2Water, to campaign "through peaceful protests and other democratic actions" against the current scheme.
Surrounded by scores of gardai and noisy but peaceful protesters outside a shopping centre in Blackrock, in Cork, Mr Kenny said he was not concerned by reports Brussels was surprised at the backlash to water charges in Ireland.
"We are very happy that Ireland will measure up here, because the scheme has been designed specifically for this purpose, and Europe's only involvement now is purely for statistical reasons," he said.
Under EU rules, Irish Water will have to bring in more than half of its income from non-government funding.
In a make-or-break test for the semi-state utility, Luxembourg-based Eurostat will decide next April if the new sums drawn up to allow for lower water charges can be rubber-stamped.
The EU statistical agency is independent and has in the past caused serious problems for countries like Greece when it has questioned budgets.
Mr Kenny also insisted the coalition had responded to all of the public's concerns.
"The Government did listen, after admitting that it certainly didn't get everything right here, and it's dealt with the question of the PPS, it's dealt with the question of bonus regimes and it's dealt with the question of what happens after 2019," he said.
Speaking in Brussels, Enterprise Minister Richard Bruton said he was confident Irish Water would pass the Eurostat test next year.
Householders will be be liable for charges of 160 euro for single adult homes and 260 euro for all other homes.
But water conservation grants of 100 euro a year mean the effective costs will be 60 euro and 160 euro respectively.
The charges, liable from January 1, will remain the same for just four years, before a review.
Originally, the Government had signalled the levy would be up to 600 euro a year for some families.
A national demonstration has been planned for Dublin on December 10.