The prime minister has sacked Stuart Nash from all of his ministerial portfolios, following another breach of the Cabinet Manual.
Nash was already on his final warning, having lost the police portfolio two weeks ago for two missteps, including criticising the judiciary.
On Tuesday evening it emerged Nash sent an email to senior business figures in 2020 while he was small business minister, which contained Cabinet discussions related to a commercial relief package being negotiated at the time.
Prime Minister Chris Hipkins said in the email, Nash expressed "both his opposition to the decision Cabinet reached and the position that other Cabinet members took". The email was sent to two of Nash's donors, which Hipkins said as commercial property owners, had "an interest in the Cabinet decision".
"That crosses a line that is totally unacceptable to me."
The Cabinet Manual states that discussions at Cabinet and Cabinet committee meetings are informal and confidential.
"This is a clear breach of collective responsibility and Cabinet confidentiality," Hipkins said.
"Stuart Nash has fundamentally breached my trust and the trust of his Cabinet colleagues and his conduct is inexcusable."
Hipkins said even if Nash was not already on a final warning, this latest revelation would have triggered his dismissal.
Hipkins revealed two of the people Nash had emailed - Troy Bowker and Greg Loveridge - were donors, but said neither of them had done anything wrong.
The issue, he said, was the perception of influence, and as both men were involved in the property industry, they had an interest in the Cabinet decision.
"Disclosing those conversations in the first place was inappropriate. The fact they were disclosed to people who donated to his campaigns, I think adds to the perceptions of a conflict but also is just utterly unacceptable," he said.
Hipkins, who admitted he was "gutted", said the decision was "a black and white issue".
"Sacking people is not easy. In this particular case, I didn't feel there was any other option though. This is absolutely inexusable."
Hipkins said he had asked Nash to reflect on his future as an MP. Nash has been MP for Napier since 2014, and if he leaves after mid-April his departure would not force a by-election.
National leader Christopher Luxon compared the breach to insider trading. He said Nash should resign from Parliament immediately, and the party was ready for a by-election.
"The breach is so serious, and so egregious, and such a big contravention of the Cabinet Manual on so many levels, that you cannot trust having Stuart Nash in your caucus as the prime minister," he said.
ACT leader David Seymour said in all instances Nash was trying to do the right thing, but he repeatedly failed to follow the rules and be honest.
Seymour was not sure this latest breach was worse than Nash's phonecall to the Police Commissioner over a judicial decision, and said that incident should have been enough for the prime minister to sack him entirely in the first place.
"He's now paying the price for his earlier indecisiveness, trying to do some dismal calculus over which breach was worse than the other. I mean, come on."
But unlike Luxon, Seymour doubted there was much public appetite for a by-election this close to the general election.
Megan Woods will take over Nash's economic development role, while David Parker will pick up oceans and fisheries and Meka Whaitiri the Hawke's Bay cyclone response.
All will be acting ministers until permanent replacements can be found.