The NSW building commissioner has blamed a "problematic" relationship between a former minister and the workplace of former deputy premier John Barilaro for his decision to quit.
David Chandler's resignation letter was made public on Thursday, and had already been sent to the state's anti-corruption body.
"My personal experience has been one where engagement with the minister (Eleni Petinos') office has been problematic," Mr Chandler wrote in his resignation letter on July 7.
He said his disintegrating relationship with Ms Petinos, who was fair trading minister at the time, was impacting confidence and momentum of industry reforms, and he had received reports that others in his department felt the same.
Mr Chandler was hired to clean up the state's building industry after a series of defects were found, including at the Sydney residential buildings Mascot Towers and Opal Tower.
When taking on the role he was confronted by "frankly horrific" circumstances in the industry, he said.
The letter was sent to the Independent Commission Against Corruption on August 1, one day after Ms Petinos was sacked from cabinet by Premier Dominic Perrottet amid allegations of bullying.
When asked for a more thorough account of Ms Petinos' sacking during question time on Thursday, the premier said ministers served in his cabinet "at my pleasure".
"In relation to the decisions I have made in respect of the ministry, ministers also serve at my pleasure," Mr Perrottet said.
Principal among Mr Chandler's woes was the relationship between Ms Petinos and Coronation Property Group, at a time when Mr Barilaro was serving as its executive director.
"These concerns crystallised at the time of the Stop Work Orders issued under the Design and Building Practitioner's Act, Declared Design Audit," Mr Chandler wrote.
The orders for the western Sydney construction site were issued in April.
Shortly after the Coronation Property site received the draft shutdown notice, Mr Chandler received a call from Ms Petinos' office. He was later sent a text message by Mr Barilaro.
"This contact came to me as a message on my personal phone requesting a meeting with me," he wrote.
He copied the message and sent it on to Secretary of the Department of Customer Relations, Emma Hogan.
He later met with Mr Barilaro to answer his questions.
Ms Petinos asked Ms Hogan to investigate Mr Chandler in June over allegations he had advised banks not to work with certain building certifiers and had misled the parliament when asked about it.
Mr Chandler was later cleared of the allegations, although he resigned the same month.
"After 50 years in this industry, my character and ethical standing has been beyond reproach," he said.
His role had recently been extended through to mid-2023, and he said he believed this was due to his good performance and industry support.
"The challenges that confronted the NSW residential apartment industry at the time of my appointment where frankly horrific and highly politically charged," he said.
Mr Perrottet could not confirm when his office received the letter, but said he personally saw the letter on Tuesday.
"When I read, or did not read the letter, is irrelevant," he told the parliament on Thursday.
"What is relevant is that appropriate action has been taken, and I am advised that appropriate action has been taken."
The premier stood by his previous claims that Ms Petinos' sacking was unrelated to Mr Chandler's resignation, and was catalysed after a discussion with the department secretary over the culture in her offices.
He insisted a conversation he had with Ms Hogan on July 31 had was not related to his decision to sack Ms Petinos.
He said the letter had been referred to the ICAC "out of an abundance of caution".
Labor's better regulation spokeswoman Courtney Houssos said the letter created further questions for the government.
"There was something that really concerned (Mr Chandler), that forced him to take such drastic action," she said.
Mr Barilaro worked as the executive director at Coronation Property from February to May.
