Associate Professor at Auckland Law School Vernon Rive.

A legal expert who was consulted on the government's law change that would prevent companies from being sued over climate change has released his advice publicly, explaining his opposition to the proposal at the time.

Associate Professor at Auckland Law School Vernon Rive told RNZ he suspects the main reason for the legislative move is to "remove the opportunity for corporate accountability" and likened stopping the case halfway through as being "constitutionally abhorrent".

RNZ reported last month that a previously undisclosed briefing document had been provided to the prime minister's office by Fonterra and Z Energy regarding climate activist Mike Smith's case against those companies and other major emitters.

RNZ also reported officials had told the government not to intervene in the court case.