This previous case - when he made public comments relating to the killing of police constable Matthew Hunt - was bad enough the Solicitor-General considered prosecuting him for contempt.
Prime Minister Chris Hipkins says the matter happened in the past and Nash is "on notice" over future breaches.
Nash told Newstalk ZB in 2020, a few days after the shooting, that Hunt's death was an "absolute tragedy."
"In true police form they have been incredibly professional. They caught the guy that did it and his accomplice very, very quickly and now they're building the case and it will go to court.
"Let's hope this guy has many years in jail to contemplate what he has done," Nash told Newstalk ZB.
A letter from Crown Law - the lawyers who act on the Crown's behalf - said the Solicitor-General had decided not to prosecute Nash over his comments but only considered the matter resolved after a formal reprimand from the Attorney-General.
"She recommended to the Attorney‐General that he speak to Minister Nash directly to convey that his comments were unacceptable and remind him not to make public comment on cases before the courts," the letter said.
The Attorney-General is the MP tasked with acting as the top lawyer for the government.
The letter said Attorney-General David Parker had granted permission to speak on his behalf about the actions he had taken.
In a statement, Hipkins said he considered the matter "in the past".
"The Attorney-General was asked by the Solicitor-General to speak to Minister Nash to convey that his comments were unacceptable," he said.
"The Attorney-General did that and the Solicitor-General considered the matter resolved to her satisfaction.
"Minister Nash has already lost his prized Police portfolio and knows he's on notice over any future serious errors of judgment."
National's Police Spokesperson Mark Mitchell said the case raised "big questions" over Nash's continued presence in Cabinet and how much Hipkins knew.
"To me now it's untenable that Stuart Nash will remain, he should have actually been stood down as a Cabinet minister the first time but now that this has come to light it's just going to open up a whole lot more questions.
"Did he [Hipkins] know about it?," Mitchell asked.
"Having a minister that can breach so seriously that the Solicitor-General was actually considering prosecution ... why on earth would he reappoint him as police minister."
In a statement, ACT leader David Seymour said Hipkins had no choice but to sack Nash entirely.
"It has now been revealed that Stuart Nash is a recidivist offender when it comes to breaching the Cabinet Manual," he said.
"Chris Hipkins has shown how low his standards are. It was bad enough that he wouldn't sack him yesterday, now that it is known Nash is a repeat offender it is unforgivable."
"The prime minister cannot have confidence in him after this. He needs to go from all of his portfolios."
Nash resigned as police minister on Wednesday after boasting about phoning the police commissioner to discuss whether a case he disagreed with the judge on would be appealed.
He had initially refused to back down on his comments about the judicial decision and said the conversation with the commissioner was just him "chewing the fat" with a "mate".
Hipkins had accepted his resignation by the time Parliament began sitting at 2pm on Wednesday afternoon, but on Thursday said he still had confidence in Nash to perform his other roles.
