SINN Féin has called on Arlene Foster to stand aside while an independent probe takes place into Stormont's botched green energy scheme.
The party has tabled an extensive amendment which effectively trumps the SDLP's bid to oust the first minister from office.
It calls for the DUP leader to leave office for at least four weeks while an "independent, time-framed, robust and transparent investigation" takes place and a preliminary report into the Renewable Heat Incentive (RHI) scandal is completed.
The SDLP has signalled that its MLAs are likely to support the amendment, which unlike the original motion can be blocked by a DUP petition of concern.
Sinn Féin wants Attorney General John Larkin to appoint an "independent judicial figure from outside this jurisdiction" to lead the inquiry.
It says the probe must be comprehensive, covering everything from RHI policy development to the conduct of ministers, special advisers and civil servants.
Conflicts of interest and the handling of whistleblowers' alerts must also be considered, Sinn Féin said.
The party wants a preliminary report published within four weeks of the inquiry beginning and a full report three months later, insisting the contents of which will not require agreement of the first and deputy first ministers or the attorney general.
Martin McGuinness said Mrs Foster's statement to the assembly on Monday did not have his approval.
"If she speaks this will be in a personal capacity and not in her role as first minister," he said.
The Foyle MLA said there was no credibility in an inquiry established solely by the DUP or in the "selective release of some documents by DUP departments".
"If the DUP does take a unilateral approach, disregarding the authority and joint nature of the Executive Office on an issue which is cross-cutting, with massive budgetary implications and which is undermining public confidence in the political institutions this will have grave consequences," Mr McGuinness said.
He said the RHI crisis was not about party politics, nor was it an "orange or green issue".
An SDLP spokesman said pride had prevented the first minister from standing aside and pride had stopped Sinn Féin from supporting its exclusion motion.
"The public has had enough of politicians putting their own pride first and the public interest second," the spokesman said.
"This is a time to restore faith in our institutions."
The DUP leader launched the botched £1.2 billion subsidy scheme while minister for enterprise, trade and investment.
The decision not to impose a cap on payments like a corresponding scheme in Britain is regarded as the RHI's key flaw.
The failure to put any cost control measures in place means a £400m hole will be burned in the Stormont executive's budget over the next 20 years.
