SDLP leader Colum Eastwood says First Minister Arlene Foster should “step aside for a period” while claims around the botched RHI energy scheme are investigated.
The Foyle MLA said “confidence was being drained” from the political institutions in Northern Ireland.
“The only way we can find out the truth now is if all the documents that have been referred to are put into the public domain,” he said.
The party is to put before the Assembly on Monday a ‘Motion of No Confidence’ in the First Minister.
It needs 30 signatures but Sinn Fein have not yet said whether it will support the motion.
Mr Eastwood was speaking following claims made to Stephen Nolan on BBC 1 NI interview with former DUP Enterprise Minister Jonathan Bell on Thursday night.
He claimed the First Minister stopped him from closing down the RHI scheme as it was becoming too costly.
The DUP MLA said his party boss “ordered him” to keep the scheme open for a further two weeks
And he accused DUP Special Advisers (SPADs) of interfering with a paper trail to keep his party leader’s name out of the RHI scandal
But the First Minister and the SPADs have denied Mr Bell’s claims.
Mr Bell now faces an internal disciplinary inquiry by DUP officers for breaching rules in speaking to the Nolan show over the row without consulting the party.