NZ First MP Andrew Williams has started legal proceedings over being dumped from the party list ahead of the election.
Williams is seeking a declaration that the party breached its constitution when it determined the list, removing him as an electorate (East Coast Bays) and list candidate.
Williams had been ranked number 3 on the party list in 2011, and said he was given no reason for his demotion.
"I regret that I have no other option other than to take my party to Court to protect my reputation", Williams said.
He had been "mistreated" by the party.
"I do not, however, wish to derail NZ First's campaign, so I am asking for an urgent hearing following the election.
"As the matter is now before the Court, I do not intend to make further comment."
Party leader Winston Peters was not aware of Williams filing legal proceedings this afternoon. He had not been served with a writ.
He said Williams didn't understand the party's constitution, the legal precedent or the process if he was taking court action.
Peters laughed off suggestions he had lost control of his caucus and said it was inevitable some people would be upset with their list rankings.
University of Otago law professor Andrew Geddis said the precedent in a case like this had ironically been set by Peters, when he was in the process of being dumped by National.
The court accepted Peters could challenge actions of the party, but at the same time took a narrow procedural approach to the issue.
It would be a matter of the court examining NZ First's constitution and seeing what allowed it to take the step of dumping Williams, Geddis said.
Even if a court decided the process was flawed, it would have to decide on a remedy.
"And is a court really going to order NZ First to stick a guy who is right on the outer with them back on their list?
"What they can just say is the party has breached its rules, and just basically leave it at that. It's going to be a hard ask," Geddis said.
Peters said earlier this week he was "very concerned" about Williams' comments surrounding a draft list, saying they breached a confidentiality agreement that all engaged in the process had been required to sign.
It is understood Williams was removed from the selection process from NZ First because of the comments, with the party believing it made him ineligible to be an MP.