Shane Jones Photo: RNZ / Samuel Rillstone
Ministers' public statements about judges amount to attacks on the judiciary, barristers say.
The New Zealand Bar Association said there had been a recent increase in such statements and it was concerned at the risk of political interference in the courts.
It followed reports that Fisheries Minister Shane Jones called a High Court judge a "communist judge"during a meeting with the seafood industry.
When asked about the comment, ime Minster Christopher Luxon said Jones was "being descriptive, not critical".
Association president Maria Dew said the comments could not be explained away as "political rhetoric" by politicians "when ministers of the Crown owe duties to uphold the role of judges".
She said judges could be an easy target as they could not defend themselves or their judgments.
"The careful separation and balance of powers between our courts, government and politicians means ministers must not engage in any personal criticism of judges or the leadership of the courts. Just as the courts and judges remain outside of politics."
Dew said New Zealand did not want to follow the example of other countries where political interference saw courts lose their independence.
"It is fundamental for our democracy that judges are not the subject of personal attack or criticism by ministers that may risk judges being restricted in their role.
"Judges must be capable of being able to freely play their independent constitutional role in Aotearoa New Zealand."
Dew urged the government to make sure the ministerial conduct was not condoned by inaction, and was writing to attorney-general Judith Collins seeking action against MPs' behaviour.