Labour Party leader Phil Goff says Chris Carter has no credibility and it is time for the MP to move on.
Labour's ruling council decided to expel the Te Atatu MP from the party on Monday night over his attempts to undermine Mr Goff, starting with an anonymous letter sent to the media in July.
It says Mr Carter had bought the party into disrepute.
Mr Carter has claimed that he met with three other Labour MPs the night before the letter was sent and discussed when a leadership coup should take place.
He also claimed there were 17 people within the Labour Caucus who would vote against Mr Goff.
However, Mr Goff says the now independent MP is lying.
"There is no substance, there's no evidence for it. What there is evidence for is, unanimously, the Labour Party Caucus decided to sack him from the Caucus and ... the ruling body of the Labour Party made the same decision."
Meanwhile, Labour MPs have been warned some Caucus members may be inadvertently dragged into the row.
Party president Andrew Little says over the past few months some of the party's MPs have been in contact with Mr Carter to show support for him personally.
He says Mr Carter has interpreted that as being support for his idea of a coup against Mr Goff.