The Sinn Féin 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 powersharing administration depended on his party’s agreement.
Addressing party faithful in west Belfast, Mr Adams left little doubt that Sinn Féin will pull the plug on the institutions if Mrs Foster does not temporarily step down over the so-called ‘cash for ash’ scandal. That would likely prompt a snap election.
Mrs Foster, who presided over the Renewable Heat Incentive when she was economy minister, has steadfastly refused to leave the stage to facilitate a probe into a scandal that has left Stormont facing a £490m (€570m) 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 Féin will bring this ongoing and totally unacceptable state of affairs to an end.”
The fate of the current administration now hangs on whether or not Mrs Foster will stand down.
On Friday, she voiced support for a judge-led probe into the renewable heat scheme outlined by her Sinn Féin partners in government, but again emphatically rejected Sinn Féin’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 Renewable Heat Incentive was supposed to offer a proportion of the cost that 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 £1m in the next two decades for heating an empty shed.
The total spend for the scheme in Northern Ireland is estimated at £1.15bn (€1.34bn) 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 Féin has 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 Renewable Heat Incentive scandal. She repeated that refusal on Friday.
“That is not good enough. Arlene Foster has been first minister for almost a year.
“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 Féin allows it.”
In a strongly worded speech, Mr Adams also called DUP Communities Minister Paul Givan an “ignoramus” for cutting funding for an Irish language initiative.