Climate change activist Mike Smith has filed High Court proceedings challenging the government's decision to block tort-based climate change litigation.

Smith is seeking a declaration that the government's intervention and the procedural steps leading to it were unlawful. The challenge follows the government's move to change the law to prevent companies being sued over greenhouse gas emissions through tort-based litigation.

The blocked lawsuit

Smith had been pursuing legal action against six emitters including Fonterra and Z Energy, with the case due to be heard in April.

Justice Minister Paul Goldsmith intervened to halt the proceedings, announcing the legislative change would cover both existing and future cases. Goldsmith said at the time the litigation was "creating uncertainty in business confidence and investments that the government must address".

The minister also argued the change would prevent development of a new regime contradicting Parliament's existing climate change framework.

Corporate briefing and official advice

A previously undisclosed briefing document from Fonterra and Z Energy about Smith's case was provided to the prime minister's office.

Despite this corporate engagement, government officials recommended against intervening in the court case.

Smith alleges the government acted unlawfully by stepping into live court proceedings without following proper process. "Something has gone seriously wrong here," he said.

"The government decided to introduce this legislation after the defendants lobbied for it. Their lobbying efforts disappeared from the public record," Smith said.

Process concerns

Goldsmith did not notify Smith or hear from him before making the decision to block the litigation.

Smith wrote to Prime Minister Christopher Luxon on 28 May seeking a meeting about how Luxon's office handled the case but received no response.

Goldsmith declined to comment when approached by RNZ about Smith's High Court proceedings.

Academic criticism

Auckland University Associate Professor Vernon Rive, who was consulted during the government's planning, advised officials that the likelihood of a contradictory regime emerging was very low.

Rive described stopping Smith's case partway through as "constitutionally abhorrent".