Despite not agreeing with all of his actions in the role, the treatment of the resigning David Chandler demonstrates double standards, the NSW branch of the Construction, Forestry, Mining and Energy Union said in a statement on Thursday.
"It was well known in the industry that he was attempting to uphold building standards in construction and trying to ensure dodgy builders were held responsible for defects in properties they built," the union's state construction secretary Darren Greenfield said.
It appeared he upset some members of the government in doing so, Mr Greenfield said.
The public should question whether Mr Chandler was undermined in the role, he said.
Mr Chandler resigned on July 7, in a letter noting a "problematic" relationship with former fair trading minister Eleni Petinos, among other concerns.
Department of Premier and Cabinet secretary Michael Coutts-Trotter was told of his decision by the Department of Customer Service secretary Emma Hogan on the day it happened.
"His resignation letter is not flattering of the minister ... would certainly appreciate your wise advice here," Ms Hogan wrote in a text message that day, which was released through parliament on Thursday.
A follow-up text message about seven hours later gave the "heads up" that media had inquired about a property group named in Mr Chandler's resignation letter, who Ms Petinos had met with twice in the previous month.
The letter was sent to the Independent Commission Against Corruption on August 1 and parliament ordered its release on August 11.
Ms Petinos was sacked over bullying allegations, four hours after the building commissioner's letter was sent to the premier's chief of staff but before Premier Dominic Perrottet first read the letter on August 10.
He had been advised the matter had been dealt with appropriately by Ms Hogan in a meeting on the day Ms Petinos was sacked.
The meeting was primarily focused on her workplace behaviour and the letter was only raised as a "peripheral" issue, the premier said.
With the minister gone, attention has turned to whether Mr Chandler could be convinced to stay.
Mr Perrottet said on Wednesday he expected the state to have a building commissioner by the time Mr Chandler was scheduled to finish at the end of November.
He did not indicate who the likely candidate was.
"That's not a matter I can answer today," he said.
"What is important is that we have a building commissioner in place.
"David Chandler has been a very strong building commissioner," he said.
