Greens candidate David Hay has been suspended from the party for a year after challenging Russel Norman for the co-leadership.
Hay stood for the party in the Epsom electorate in 2011, but fell out of favour last year when he went after Norman's job.
In December, he said both Norman and co-leader Metiria Turei had betrayed the Greens' core principles and should resign.
In a statement issued this morning the party confirmed his membership was suspended "following an investigation into misconduct."
A panel found his behaviour breached party rules. A report recommended a "cooling down" period of one year, after which Hay can reapply for membership.
It said Hay admitted breaking the rules by attacking the leadership through the media and releasing internal party documents.
But the report also found he had a genuine grievance because he was barred from the candidate pool based on some allegations of which there was no evidence.
The report added: "He could be a valuable member after some reflection on what it takes to be part of a team."
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