The government has sent the controversial letter to the state's anti-corruption body, and a successful motion securing its public release will see the letter published before midday on Thursday.
Premier Dominic Perrottet said during Question Time on Wednesday he had read David Chandler's letter, and it would be provided to the upper house on Thursday.
"This is a letter related to an employment matter," he told parliament.
"Out of an abundance of caution the letter was provided to the ICAC (Independent Commission Against Corruption) for information."
The letter was sent to the ICAC on August 1, one day after Ms Petinos was sacked as a minister amid bullying allegations.
The premier said he become aware the letter had been sent to the ICAC on Tuesday night.
Labor successfully managed to force the government to release the letter from Mr Chandler, who tendered his resignation in June and will finish in November.
Mr Chandler reportedly wrote that his concerns about Ms Petinos' office escalated after he issued a stop work order for a work site in Merrylands in western Sydney, according extracts published by News Corp.
"These concerns crystallised at the time of the stop work orders issued under the Building Act," the letter reportedly said.
"I received a call (from Ms Petinos' office) shortly after a draft order was issued on the Coronation Merrylands' development site."
Former deputy premier John Barilaro worked briefly for Coronation Property earlier this year.
All emails, texts and instant messages sent in the past eight months between then fair trading minister Eleni Petinos, her current and former staffers, Mr Barilaro and Mr Chandler will also be released on Thursday.
Mr Chandler was hired to clean up the state's building industry after a series of high-profile defects were found, including at the Sydney residential buildings Mascot Towers and Opal Tower.
The premier on Wednesday reiterated that Ms Petinos' sacking was not related to Mr Chandler's resignation and said he himself was not involved in the matter.
Labor leader Chris Minns pointed out Ms Petinos was "effectively" sacked on July 31, and the letter referred to ICAC on August 1.
AAP understands Ms Petinos has not seen the letter and cannot comment on it.
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