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Mr Walker said on Saturday he could not abide by the party’s rules which did not allow him to speak freely.
"I had to sign a belt-and-braces [agreement that] thou shalt only say what we tell you to say and nothing else."
Mr Walker had been selected to stand for the party in the Southland electorate, but was now in the process of registering as a candidate for Invercargill.
He was focused on finding a way to stop the closure of the Tiwai Point aluminium smelter.
Meanwhile, the Green Party has announced a new candidate for the Waitaki seat.
Dr Sampsa Kiuru, who lives in Clyde with his family, said Waitaki covered a large area of the Central Otago, Queenstown Lakes and Waitaki Districts which had many issues in common, including the provision of sufficient healthcare.
"The Green Party will push any government to go further and faster to address inequality as we began to do with the Wellbeing Budget," he said in a statement.