Former deputy Prime Minister Winston Peters says he will seek a judicial review of the decision to trespass him from Parliament.
"This is not about whether former Members of Parliament should be treated differently to others who were at the protest – they should not. This is about fairness, freedoms, democracy, and one law for all New Zealanders," he said in a statement.
"It is my intention to seek a precedent on behalf of the hundreds of others who were unreasonably and therefore unlawfully trespassed for peacefully protesting."
He says he has consulted with lawyers and will be setting up "a way to sign up to support this action and to help fund its costs".
"Watch this space," he tweeted.
Prime Minister Jacinda Ardern on Tuesday spoke to Speaker Trevor Mallard about the decision to trespass Peters, who toured the parliamentary protest site one day in February.
That led MPs from across the House to meet to decide whether former MPs should be treated differently to others in terms of being trespassed. Mallard later said only ACT supported that exemption.
While Mallard claimed to have delegated authority to Parliamentary security to make decisions about the trespass notices, Ardern said the decision ultimately sat with the Speaker.
"I think it is useful for all parties to be able to hear him out on how he came to the decision and make a joint decision, as much as they are able to, on whether or not MPs should be treated differently from everyone else. That's, at the heart of it, the issue."
Peters on Tuesday slammed Mallard's "dictatorial behaviour" and said it was "astonishing" former MPs, including some planning to run at next year's election, were being trespassed. He also said there was a difference between those who actively participated in the protest and those who just visited.
Also trespassed is former National MP Matt King who visited the protest on two instances and spoke. King called the decision "undemocratic" and promised to fight it.
The anti-vaccine mandate protest took over Parliament's grounds and surrounding streets throughout February and early March. They stayed for weeks despite police, the Speaker and MPs telling them to leave.
ACT leader David Seymour told reporters on Tuesday afternoon that Mallard's "petulance and pettiness seems to be at the heart of so much drama" and predicts court cases will result from his actions.
Greens co-leader Marama Davidson said it doesn't matter whether those trespassed are former MPs or not, and there are consequences for people's actions. Fellow co-leader James Shaw agreed it's important former MPs "don't get an exception".
Christopher Luxon, the National Party leader, pointed out King is no longer a member of National - King resigned earlier this year and launched his own party - and the decision to send him a trespass notice was one for the Speaker.
"Those are issues fundamentally for the Speaker and the trespass laws that are sitting in this place around Parliament," Luxon replied.