The Independent Broad-based Anti-Corruption Commission has been investigating the United Firefighters Union's role in Victoria's fire services reform since 2019.

But The Age on Wednesday revealed the watchdog is also examining Mr Andrews and a senior public servant's interactions with the union and has interviewed several former and serving Labor MPs and staffers.

Speaking outside parliament, Mr Andrews repeatedly declined to confirm whether he was being investigated by the watchdog.

Legally, he may not be able to, as it can be an offence for individuals to confirm that they have been interviewed by IBAC or are subject to an investigation.

"If you want to know what's going on at IBAC, who they're talking to and what they're talking to them about, then you should go and have a chat to IBAC," he told reporters on Wednesday.

"In everything I do, I behave appropriately. I'm very conscious of the oath that I swore and the duty I have to every single Victorian and to suggest otherwise is completely wrong."

The commission refused to comment on The Age's report.

"As a matter of practice, IBAC does not comment on whether it has a complaint or investigation before it," it said in a statement to AAP.

Mr Andrews said he had not spoken to UFU secretary Peter Marshall in more than a year and that he was proud of the government's reforms to the fire services, which involved merging of Metropolitan Fire Brigade members and career Country Fire Authority firefighters into the new Fire Rescue Victoria.

The UFU championed the reforms, while volunteer firefighters and the Victorian opposition said it would hand the union too much power.

The reforms passed parliament with the help of crossbenchers in 2019 after more than four years of negotiations between the government, the fire services and the union, during which Mr Andrews reportedly intervened.

Emergency services minister Jane Garrett, CFA chief executive Lucinda Nolan and chief fire officer Joe Buffone all quit while the board was sacked amid the dispute, as they opposed the deal.

Opposition Leader Matthew Guy and shadow attorney-general Tim Smith have called on the premier to resign if he is being investigated.

"The former premier of NSW resigned because she was under investigation by ICAC. The premier of Victoria is under investigation by our anti-corruption commission, IBAC, why hasn't the premier stood down?" Mr Smith told reporters.

"I'm delighted that IBAC is finally going to look into the very murky, ugly, nasty underbelly of the Labor party, and their insidious relationship with this brutally awful union."

When asked if he would stand down pending the outcome of an IBAC investigation, Mr Andrews replied: "Absolutely not".

"I will not be doing anything other than my duty and what I'm sworn to do and that is to work as hard as I can to deliver on my commitments to the community, keep the community safe and make sure that we can deliver our roadmap to opening," he said.

Next week, IBAC will begin public hearings into allegations of branch stacking in the Labor Party.

Australian Associated Press