Gerry Adams has made clear Sinn Fein will not back down from its demand for Stormont First Minister Arlene Foster to stand aside to allow a probe into her role in a botched green energy scheme.
The Sinn Fein president warned the Democratic Unionist leader that she is not a "Prime Minister" and her position in one of the two leading roles in the power-sharing administration depended on his party's agreement.
Addressing party faithful in west Belfast, Mr Adams left little doubt that Sinn Fein will pull the plug on the institutions - likely prompting a snap election - if Mrs Foster does not temporarily step down.
Mrs Foster, who presided over the Renewable Heat Incentive (RHI) when economy minister, has steadfastly refused to leave the stage to facilitate a probe into a scandal that has left Stormont facing a £490 million bill.
Mr Adams said: "If the First Minister does not take the actions that society desires and deserves and which a sustainable process of change requires, then Sinn Fein will bring this ongoing and totally unacceptable state of affairs to an end."
The fate of the current administration now hangs on the pivotal issue of whether or not Mrs Foster will stand down.
On Friday she voiced support for a judge-led probe into RHI outlined by her Sinn Fein partners in government, but she again emphatically rejected the republican party's prerequisite that she step aside to facilitate it.
"It is clear there are many in the political class who do not believe in due process or natural justice," said the DUP leader.
"They just want me to go regardless of the fact that there is not a scintilla of evidence of wrongdoing against me. I don't roll over to my political opponents."
The state-funded RHI was supposed to offer a proportion of the cost businesses had to pay to run eco-friendly boilers, but the subsidy tariffs were set too high and, without a cap, it ended up paying out significantly more than the price of fuel.
This enabled applicants to "burn to earn" - getting free heat and making a profit as they did it.
Claims of widespread abuse include a farmer allegedly set to pocket around £1 million in the next two decades for heating an empty shed.
It was originally envisaged that the Treasury would foot the bill for the RHI, but the costs spiralled well beyond London's financial commitment.
The total RHI spend in Northern Ireland is estimated at £1,150 million over the next 20 years.
The lack of consensus over the form of an investigation comes amid similar disagreement on DUP proposals to reduce the overspend. The DUP has claimed its proposals could wipe out the bill, but Sinn Fein have rubbished them.
In his speech on Saturday, Mr Adams said: "The DUP leader has thus far refused to stand aside, without prejudice, pending a preliminary report by an independent investigation into the RHI scandal.
"She repeated that refusal yesterday.
"That is not good enough. Arlene Foster has been First Minister for almost a year."
He added: "Arlene Foster is not a Prime Minister. She is a co-equal partner in the Office of First and Deputy First Minister. She can continue in that office but only for as long as Sinn Fein allows it."
In a strongly-worded speech he also branded DUP Communities Minister Paul Givan an "ignoramus" for cutting funding for an Irish language initiative just before Christmas.
He said during 10 years of partnership government together, the DUP had shown Sinn Fein "deliberate provocation, arrogance and disrespect".