Premier Dominic Perrottet said during question time 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 on Wednesday.

"Out of an abundance of caution the letter was provided to the ICAC (Independent Commission Against Corruption) for information.

"I understand the letter is to be provided to the upper house tomorrow."

Mr Perrottet did not say when the letter was sent to the corruption watchdog but when asked when he was made aware the letter had been referred to ICAC, he replied: "Late last night."

NSW Labor is forcing the release of the letter from Building Commissioner David Chandler, who tendered his resignation in June and will finish in November.

The construction industry veteran was hired to clean up the state's industry after a series of high-profile defects were found, including at the Sydney residential buildings Mascot Towers and Opal Tower.

News Corp reports Mr Chandler cited a "problematic" relationship with former fair trading minister Eleni Petinos as one reason he quit.

Mr Perrottet sacked Ms Petinos from her portfolios 10 days ago, amid allegations of bullying and an "unsafe" environment in her office.

Labor MP Courtney Houssos introduced a motion that passed parliament on Wednesday, to force the letter's public release within 24 hours.

All emails, texts and instant messages sent in the past eight months between Ms Petinos, her current and former staffers, former deputy premier John Barilaro and Mr Chandler will also be released.

Labor Leader Chris Minns said on Wednesday morning he intended to ask the premier during question time why he had not read Mr Chandler's resignation letter.

"Despite the fact that we've known about this resignation for weeks and weeks, he (Mr Perrottet) informed the parliament that he had not read it," Mr Minns said.

The letter reportedly cites development company Coronation Property, where Mr Barilaro briefly worked earlier this year, as one of Mr Chandler's gripes.

Reports say Coronation Property hosted a meeting between Ms Petinos and Mr Barilaro on June 21, weeks before a building ban on a $500 million Coronation Property development was lifted.

Leader of the government in the upper house Damien Tudehope confirmed he also had not read the letter.

The premier on Wednesday reiterated Ms Petinos' sacking was not related to Mr Chandler's resignation and that he himself was not involved in the matter.

Mr 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.

Australian Associated Press