GERRY Adams has urged Arlene Foster to step aside with a warning that the Stormont institutions are at a "defining point".
The Sinn Féin leader's comments came after his DUP counterpart again refused to vacate the first minister's office while an investigation takes place into her oversight of the Renewable Heat Incentive (RHI).
The Louth TD's remarks are the latest in a series of verbal ultimatums from senior Sinn Féin figures aimed at the DUP leader.
Before Christmas Martin McGuinness warned of "grave consequences" if the first minister acted unilaterally in a bid to address the executive's RHI overspend, while earlier this week the party's chairman Declan Kearney said relations between Stormont's main partners had reached a "tipping point".
The Sinn Féin leader's comments echoed Mr Kearney's broad criticism of the DUP's record in government, as well as focusing on the RHI crisis.
Mr Adams said the first minister could not help but be aware of how her insistence on remaining in office was damaging public confidence.
"Yet the DUP chooses to ignore the public outrage over the RHI affair and the potential loss of over half a billion pounds to the executive's budget during the next 20 years," the Louth TD said in a statement.
He said the assembly would debate Sinn Féin's motion on the RHI on Monday January 16, where a call for Mrs Foster to step aside will be repeated.
"But whatever the outcome of that debate, the reality is that the political institutions have reached a defining point," he said.
"Neither the public nor Sinn Féin can continue to countenance the manner in which the DUP conduct business within the executive and the assembly."
Mr Adams said the immediate crisis could be resolved but it would "require Arlene Foster to do what Peter Robinson did".
"She should step aside to facilitate an independent process which gets to the facts of the RHI scandal effectively and quickly," he said.
"This is a straight forward case. The first minister has been in office for a relatively short time. If she wants to continue in that office she needs to do the right thing."
The former West Belfast MP said Sinn Féin had kept faith with the Stormont institutions and that over the past ten years the party's assembly team had navigated its way through a "number of crises and scandals". He said a lot of good work had been done on many issues, including on cross border and all-Ireland matters.
But he said there had been little or no progress on other issues.
"I'm thinking here of the long standing absence of a bill of rights," he said.
"There has also been a shameful lack of respect accorded to the Irish language and to those citizens who wish to live their lives through Gaeilge… the reprehensible decision on the eve of Christmas to cut funding for the Líofa programme is just one example of this."
Other issues Mr Adams highlighted as reflecting badly on the DUP included Peter Robinson reneging on a commitment to build a peace centre at on the former Maze-Long Kesh site, the DUP’s "resistance" to the legacy and truth recovery mechanisms of the Stormont House agreement, and what he described as "the Project Eagle debacle".
