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The Greens launched an investigation in November after Mr Hay challenged for the leadership of the party.
A panel found that he had breached the party's code of conduct and recommended a "cooling down" period of one year.
A report by the panel said Mr Hay had admitted breaching party rules by releasing internal documents which related to the process of choosing candidates.
He had also attacked co-leaders Russel Norman and Metiria Turei in press statements.
Mr Hay was ranked 16th on Greens' list and ran as a candidate in the 2008 and 2011 elections.
After he failed to make it through a vetting process to become a candidate in this year's election, he made a challenge for the leadership of the party.
The panel told him any member was entitled to challenge for the leadership at any time, but he had not considered the effect on the party in an election year.
The report said Mr Hay was upset about allegations made about him within the party, such as claims he went against party strategy by seeking the electorate vote in Epsom in 2011.
He also felt his formal complaints had been ignored.
- By Isaac Davison of the NZ Herald