Ulster Unionist leader Mike Nesbitt has said the next steps needed to deal with overspend in the botched Renewable Heat Incentive (RHI) scheme are clear but that Arlene Foster must resign to restore public confidence in the institutions.
Mr Nesbitt called on the First Minister to show "true, selfless leadership" and stand down saying it is a 'fresh crisis, not a fresh start".
He said: "The next steps are clear. We should fix the flaw in the Renewable Heat Incentive scheme by the Assembly legislating to introduce the cost controls that should have been there in the first place, while the Executive should ask Westminster to bring in a Windfall Tax to recoup the excessive profits made to date.
"In parallel, Mrs Foster should show true, selfless leadership and resign as the first step to restoring public confidence in the integrity of the institutions.
"Those steps may be obvious, but it appears equally clear this evening that we are off in a quite different direction, into another cul-de-sac of petty party political point scoring, with the DUP and Sinn Féin incapable of delivering the promised Fresh Start.
"This is a fresh crisis, not a fresh start, and if it leads to an Assembly Election, I hope people reflect on the last ten years of DUP / Sinn Féin rule and recognise that with the introduction of an Official Opposition at Stormont, there is for once an opportunity to vote for change."
Meanwhile DUP Economy Minister Simon Hamilton and Sinn Fein Finance Minister Mairtin O'Muilleoir held talks over how to cut the projected £490m overspend.
The two ministers clashed over how to deal with the continued spending on the flawed scheme which pays out £1.60 to businesses for every pound they spend on fueling biomass boilers.
A DUP plan to bring emergency legislation was announced on Wednesday by the party.
However, Mr O'Muilleoir said he was "bemused" to read of the plan in the media given how any proposal needs his approval.
On Thursday, the Sinn Fein MLA tweeted: "Disappointed that after 7 months of asking still no plan to tackle RHI mess. 'Interim solution' sticking plaster approach won’t cut it."
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 to be more than £1 billion over the next 20 years.
The Treasury is set to cover £660 million of that, with Stormont landed with the remaining £490 million.