Suspended Labour MP Chris Carter is unrepentant about his attack on Phil Goff's leadership, which may have cost him his political career.
Caucus members voted unanimously to suspend Mr Carter on Thursday after he admitted sending an anonymous letter to journalists claiming growing discontent with Mr Goff's performance.
Mr Carter told Morning Report that he wants Labour to win the next election and the party is not going to be able to do that with Mr Goff at the helm.
Senior Labour MP Trevor Mallard told Morning Report Mr Carter's actions were probably triggered by pressure over his expenses and an unsanctioned trip to Tibet.
Mr Carter refused to discuss the trip on Morning Report.
He also refused to say who he thought should lead the Labour Party, but said it's inevitable that Mr Goff will be toppled.
Earlier, Mr Carter said he will not resign as the MP for Te Atatu and would continue to vote with Labour in Parliament.
Actions 'stupid' - Goff
Mr Goff says he is confident there will be no challenge to his leadership before the next election.
He told Nine to Noon the situation is humiliating for Mr Carter.
Earlier, he said no one in the caucus supported Mr Carter and described his actions as disloyal, dishonest and stupid.
Mr Goff said he will recommend to Labour's national council that it suspends Mr Carter's party membership and selects another candidate for Te Atatu. The council meets in a week.
Labour Party president Andrew Little says the matter is a big set-back for the party.
He told Morning Report the caucus had been getting good traction on a number of issues lately and Mr Carter's actions have blown a lot of this work out of the water.
Radio New Zealand's political editor says Mr Carter's actions will mark the end of his time in politics, as "there is no way back" and "he is clearly under stress".
On Morning Report, Mr Mallard described the bid to undermine Mr Goff's leadership as political suicide.