Senior Democratic Unionist Jonathan Bell has been suspended from the party.
It followed the former Stormont enterprise, trade and investment minister’s outspoken comments about leader Arlene Foster’s handling of a green energy incentive scheme which critics predict will overspend by £400 million.
DUP party officers met over the weekend and a spokesman confirmed the Strangford Assembly member’s suspension was unanimously agreed.
On Monday the Assembly will discuss a vote of no confidence in the First Minister.
Her Sinn Fein deputy Martin McGuinness has asked her to step aside to allow a probe into allegations surrounding the Renewable Heat Incentive (RHI) scheme.
The row threatening the peace-building institutions has erupted over the controversial green energy scheme - set up by Mrs Foster - which paid out subsidies well in excess of the costs of buying renewable fuel.
Claims of widespread abuse include a farmer allegedly set to pocket around £1 million in the next 20 years for heating an empty shed.
The “cash for ash” scandal reached fever pitch when Mr Bell broke ranks to level a series of explosive claims against his leader Mrs Foster and party advisers.
In an extraordinary TV interview, a tearful Mr Bell said God told him to come clean as he claimed a “highly agitated and angry” Mrs Foster demanded he keep the RHI open for an extra fortnight despite its huge losses.