Rob Campbell says his removal from the Environmental Protection Authority is "Muldoonism in action", and thinks it unrelated to his social media post.
But Public Service Commissioner Peter Hughes has advised the government Campbell's comment was a clear breach of conduct.
Campbell has been removed as chair of the Environmental Protection Authority, just days after his firing from the same position at Te Whatu Ora - Health NZ.
The government had been under pressure over Campbell's positions after he posted criticism on social media of the National Party's policy on water infrastructure, its answer to the government's Three Waters legislation.
In announcing Campbell's firing from the EPA - which also includes his board membership - Environment Minister David Parker said he had taken advice from the Public Service Commissioner that the comments were a clear breach of Code of Conduct requirements for such roles.
Campbell told RNZ he did not think it had much to do with the post.
"I'm very disappointed to be not working alongside the team at EPA anymore, and I'm disappointed in the attitudes that lie behind the minister's decision," he said.
"The truth is that I can say things now I could not say when I was a public servant, so I'll say them: The only disagreement I ever had with Minister [of Health Ayesha] Verrall was about a request to tone down my public statements about Te Aka Whai Ora (the Māori Health Authority), and the role of Māori in health governance."
He said his only disagreement with Parker had been related to a similar matter regarding the work of Ngā Kaihautū Tikanga Taiao, the Māori advisory group at the EPA.
"The trigger point on this is again about co-governance as an issue - the government is clearly trying to walk backwards on the public prominence of co-governance issues and they don't like me promoting those so I think it's pretty clear what this issue is about."
However, these assertions appear to contradict Campbell's letter to Parker in response to the accusations, which said the matter over his criticism of National's Three Waters policy was the first and only disagreement they had.
In the same document, Campbell said this made the situation with the EPA different to the one at Te Whatu Ora because "Minister Verrall was of the view that on a couple of previous occasions, matters about my public commentary had been raised with me".
Another letter from Public Service Commissioner Peter Hughes to both Parker and Verrall shows his advice was clear the public service should remain politically neutral - a longstanding convention which was set down in law in 2020.
The code requires public servants to act in a way that means they can work effectively under current and future governments, including not making political statements or engaging in political activity related to the functions of the entity they represent.
"When acting in our private capacity, we avoid any political activity that could jeopardise our ability to perform our role or which could erode the public's trust in the entity," the code says.
Hughes said Campbell's post suggested National's policy should not be taken seriously, and called party leader Christopher Luxon's judgement and the party's integrity into question.
"I am aware that concerns have previously been raised with Mr Campbell about past public comments he has made," Hughes wrote.
"These most recent posts are clear breaches of the Crown entity Board member Code of Conduct and also demonstrate a failure to uphold the Public Service principle of political neutrality and in my view compromise the trust and confidence he needs to operate effectively in this role."
Campbell said he interpreted the code of conduct as saying he was able to speak freely, within limitations.
"That is an interpretation I have - clearly it's not the public service commissioner's one or the government's one. Normally what you'd do in that situation is to talk through and see if there was common ground - if there wasn't you might decide to part ways, but that never happened."
Hughes' letter to the ministers had advised them to follow principles of natural justice by putting the matter to Campbell and considering his response before making a final decision, and this appears to be the process which was followed.
Parker's office told RNZ on Wednesday said a letter had been sent, and he received Campbell's response before firing him. The same approach was taken by Verrall.
Parker's response to Campbell highlighted that "we are clearly in disagreement about the meaning of the Code of Conduct for Crown Entity Board Members".
Campbell warned his dismissals were already having a chilling effect on public service employees.
"I have messages coming in by the hour from two groups of people: One of whom are people currently employed in the public service who are worried about their own social media posts and other activities they've undertaken, and are now very fearful that they will be targeted in a similar way," he said.
"And then from people in the business world where I'm also reasonably well connected still who are saying 'Why would anybody ever take on a role like that if these people are going to have such a repressive interpretation on the code of conduct, that no one would ever do it'.
"It's not a matter of me speculating that people are thinking this, it's happening as we speak."
Campbell likened it to when then-Prime Minister Robert Muldoon "publicly, very aggressively" attacked him in Parliament, calling him a communist and a dangerous subversive.
"It was a very chilling experience for me and in those days, that was a very damning thing to be said about you," he said. "The way I feel about this is exactly the same way, this feels to me like Muldoonism in action."
He said both the Health and EPA roles were very dear to his heart and he felt they belonged together along with social justice, but he was already being offered other roles - not in the public service - and he would take his time to consider those.
Minister Parker declined to comment further. Minister Verrall has been approached for comment.