Rogue Labour MP Gaurav Sharma is accusing Prime Minister Jacinda Ardern of lying about when the caucus agreed to suspend him.
Sharma was suspended from Labour's caucus earlier this week for what Ardern said had been repeated breaches of party rules.
The Labour caucus will consider a motion next Tuesday to expel Sharma, after he launched another public attack on the party's leadership Thursday night.
A spokesperson for Ardern said: "Gaurav has repeatedly breached his colleagues' trust, and caucus was clear that should there be further breaches such as this then further steps would be taken."
Sharma claimed in an interview with Newshub Thursday night, his first public comments since his suspension, the decision made by the Labour caucus was pre-determined.
He alleged the caucus had agreed to suspend him during an informal meeting of Labour MPs, that he was not invited to, on Monday night.
Speaking to Morning Report, Sharma said Ardern "had already made up her mind, as did the rest of the leadership, and the caucus".
"It's like organising a jury to sit down together with the whole court apart from the accused, and for them to meet up a day before and agree on what's going to happen. And then next day, presented as it is going to be a fair trial," Sharma said.
Ardern has stressed the decision to suspend Sharma from the Labour caucus was not predetermined.
"Natural justice is very important to our team," she said on Tuesday.
The meeting was convened as MPs felt they were unable to freely discuss the situation with Sharma present, Ardern said.
Sharma said Ardern's comments were not credible.
"There is no credibility, like, this isn't my credibility ... this is about the credibility of a nation's prime minister, who every step of the way has been lying. Even this week, lying and saying there is no predetermination while she called the meeting, in which everybody was invited, except me," he said.
RNZ contacted Ardern's office for a direct response to Sharma's allegations of lying, but her office declined.
Sharma also claimed last night he had recorded a phone conversation with a colleague, who called him after the Monday meeting to warn his fate was sealed.
Sharma said the colleague was a senior Labour MP.
The pair spent about an hour on the phone, Sharma said, and the senior MP "did most of the talking, took me through the meeting, and at many, many, multiple times talked about the predetermination".
The MP did not know at the time the phone call was being recorded, but Sharma said he had spoken to them since and they "don't have an issue with it."
The senior MP does not want to reveal their identity, Sharma said, as there was an "environment of fear, where people are stopped from talking".
Sharma claimed "many people" from Labour's caucus had told him they agreed there was bullying in the party. He would not say how many MPs had been in touch when asked.
Asked if he would stay in Parliament if he was expelled from the Labour caucus, Sharma said "look, that's an option".
"I haven't thought this through to that," he admitted.
If Sharma left Parliament, it would prompt a by-election in the Hamilton West electorate.
Labour MPs react
Cabinet minister Chris Hipkins denied Sharma's claim the decision to suspend him was predetermined.
He was disappointed Sharma had gone to the media again instead of seeking mediation.
"It's disappointing ... never like to see these sorts of things happen. He's clearly a bright and talented person who had a lot to offer.
"It's unlikely now he will have the opportunity to offer that because of the actions he himself has taken. That's sad."
Labour MP Kieran McAnulty also told Morning Report that Sharma's suspension was not predetermined.
"I was at that meeting, and that absolutely was not predetermined."
He said the meeting was an opportunity for people to share their views freely without fear of it being leaked.
"The mood of the room was very clear, but it certainly wasn't predetermined."
The Labour Party caucus is set to meet again since he was suspended. At the time, Ardern said Sharma was on his final warning and if he breached the rules again, he would be expelled.
McAnulty would not say how he would vote at the caucus meeting next week.