Fianna Fáil's Barry Cowen has said if the Government does not abide by the 'confidence and supply' agreement with his party on the issue of water charges, it could bring down the Government.
It comes after Minister for Housing, Planning, Community and Local Government Simon Coveney said he would not introduce water legislation that contravened EU directives and exposed the country to large fines.
He said any water strategy needed to have a polluter pays principle.
Fianna Fáil says fines are a distant prospect and can be averted.
Mr Cowen said that an Oireachtas committee set up to consider the issue has not concluded its work, and the intervention by Mr Coveney on the water issue was premature, political and unprecedented.
The positions of Fianna Fáil and Fine Gael on water charges held up the talks to form the minority government and it could now threaten its continuation.
Their members both sit on the committee to discuss the funding of water and it is currently veering towards abolishing all charges including charges for excessive usage, which Fine Gael strongly opposes.
Today's meeting of the Joint Committee on the Future Funding of Domestic Water Services has ended without agreement on how to proceed.
It is understood there were "testy exchanges" between Fianna Fáil and Fine Gael members at the meeting, with Fianna Fáil claiming Fine Gael was refusing to set out its position.
Both parties are now to table position papers by Friday and the committee will meet again next Tuesday.
Earlier, Mr Cowen said it was up to Fine Gael to quantify excessive usage.
He pointed to the deal with Fine Gael, which states the Government will facilitate the passage of legislation on the issue agreed by the Oireachtas.
He also said Fianna Fáil was not opposed to charging people for excessive usage but wanted to use existing legislation, which would provide for fines or imprisonment.
However, he ruled out taking thousands of people to court or reducing their water supply and he also said it was up to Fine Gael to quantify excessive usage.
Mr Cowen said he had not been convinced that there was wanton abuse of water and pointed to leakage as an issue.
He said it was not clear if the Attorney General had considered the existing legislation and his party would publish its own legal advice.
Separately, Mr Coveney said the Government was trying to find a compromise but it needed to be consistent with Ireland's legal obligations.
So far there is no sign of a compromise unless one side backs down.
Coveney 'happy' to work with compromises on water charges
Mr Coveney earlier said he is happy to work with compromises that politicians are working towards regarding water charges for "normal use" in houses.
Mr Coveney, who was before the Oireachtas committee on housing this morning, was asked by AAA-People Before Profit TD Ruth Coppinger if he was going to implement legislation to abolish water charges.
The minister said the position of the Government has been to try to find a compromise that the Dáil can support, that parties can work towards and that can be accepted broadly across society.
However, Mr Coveney said compromise needed to be consistent with Ireland's legal obligations under the water framework directive.
"All I said yesterday is that I don't see how I can introduce legislation against the advice of the Attorney General, when I know that it's likely to lead to court action by the European Commission and fines imposed on Ireland".
He said in order to be compliant with commitments under the water frame work directive, there needed to be some "polluter pays principle" with regard to the water strategy "where there is a consequence for wasting large volumes of water".
The minister said he was asked whether he would introduce legislation against the advice coming from the Attorney General's office and he reiterated that he could not do that.
Mr Coveney added that he is happy to work with all parties to find a way forward because the issue has "dogged Irish politics for far too long".
O'Dea wants to see Attorney General's advice
This morning Fianna Fáil's Willie O'Dea said he would like to see the Attorney General's advice on water charges.
Speaking on RTÉ's Morning Ireland, he said there is strong legal opinion that is contrary to that expressed by the Attorney General.
Mr O'Dea, who is a member of the water committee, added that Fianna Fáil is convinced that the Attorney General's legal opinion is incorrect and said attorney generals have "gotten it wrong in the past".
"We are very firm in our opinion, and the legal advice does bear it out, that there is a contrary legal view to that being expressed by the Attorney General and we are convinced that that view is the correct one.
"I would like to see the Attorney General's advice actually, we haven't been exposed to that - as yet.
"I think the minister has to take into account all legal opinion and there's very strong legal opinion which contradicts what the minister is telling us the Attorney General says... attorney generals have gotten it wrong in the past."
Mr O'Dea said ultimately Dáil Éireann will decide on the future of water charges and the Government has committed itself to implementing that decision.
He said he hoped that the situation can be wrapped up by the end of March.
Mr O'Dea said Fianna Fáil wanted to penalise people for excessive use of water but did not want to do so by setting up an expensive charging system, at a cost to the taxpayer.
"The way this is being presented in the media is that Fianna Fáil is not in favour of charging people or punishing people for excessive use of water. Nothing could be further from the truth.
We want to punish people who are wasting water but we don't want to do so by setting up an expensive billing and charging system.
"We want to do it by properly implementing legislation, which is already there - namely the 2007 Water Services Act, which provides for punishment for people who wilfully abuse and over use water."
Fianna Fáil stance on water charges 'return to days of populism'
Fine Gael TD for Dublin South West Colm Brophy said Fianna Fáil's stance on water is a return to the days of populism.
He said the water committee was working very well until yesterday when Fianna Fáil decided to implement a radical change of course.
Mr Brophy said Fianna Fáil was initially in favour of charging for excessive use of water and he cannot understand why the party is opposed to water meters which was a simple and effective way of measuring water usage.
He said Ireland could be forced to pay tens of millions of euro in fines if it is found to be in breach of an EU directive on water.
Meanwhile, Fine Gael TD for Dún Laoghaire Seán Barrett has said failure to bring back water charges means there will not be a reduction in the high-level of direct taxes in Ireland.
Speaking on RTÉ's Today with Sean O'Rourke, the former ceann comhairle said the only way to reduce pressure on PAYE workers would be to introduce indirect taxes, such as water charges.
Mr Barrett said he was in favour of the PAYE earner getting relief and he believed everyone should pay for services like water and electricity.
He said that if water charges were not re-introduced, then those who have already paid should be repaid, adding that you either abide by the law of the land or you do not.
He declined to comment on who he would back as the next leader of Fine Gael and said it was wrong to be seen to be forcing Taoiseach Enda Kenny out of office when he has given such good service to the party and the country.