In an incendiary interview on ABC Melbourne, union secretary Peter Marshall has accused Premier Daniel Andrews and Deputy Premier James Merlino of lying to him by appointing British fire chief Dan Stephens as the new head of the fire services.

Mr Marshall also declined to rule out rumours that he has a compromising tape of Mr Andrews.

“You’d have to ask Dan Andrews that, not me,” he told the ABC’s Raf Epstein.

“The truth will come out about Daniel Andrews and James Merlino’s role in this and exactly why they’ve chosen to engage in an extremely provocative appointment,” Mr Marshall said.

“There was a number of promises and they will come out in the near future … there were discussions which will come out in the near future.”

Asked if there was any deal with the firefighters' union or if the Premier was aware of any recording, a government spokesman said no.

The interview sent shockwaves through Labor ranks on Wednesday night with one frontbencher telling The Age that while he expected a difficult couple of days, Mr Marshall's demands in relation to the new Chief Officer could not be accepted.

The firebrand union chief earlier accused the government of shattering the faith that firefighters put in the Andrews government.

In a bulletin issued to United Firefighters Union members on Wednesday, Mr Marshall said the union had been assured it would be consulted prior to the appointment of the next chief of the Metropolitan Fire Brigade.

“The UFU was not consulted and is yet to be officially informed that Mr Stephens has been appointed,” the bulletin said.

Mr Marshall said the man chosen for the MFB's top job, Englishman Dan Stephens, had a “union-busting, budget-breaking” track record in his previous job as Mersey Fire Brigade chief in the northern English city of Liverpool, and had presided over savage cuts to firefighter numbers in the city.

Mr Marshall also alleged that fire deaths in the Liverpool area had doubled during Mr Stephen’s tenure.

But the Liverpool Echo newspaper reported this week Mr Stephens was known for his fierce opposition to government-imposed budget cuts.

And both the MFB and Emergency Services Minister James Merlino said on Wednesday that their new man had a strong record of advocating for his workforces.

MFB board president Jasmine Doak said Mr Stephens had a wealth of experience in firefighting, emergency services and with unions.

"Dan has a great relationship with the [Fire Brigades Union] in the UK at the moment, he works in a unionised workforce and he knows how important that is," Ms Doak said.

"He will build all the relationships he needs once he gets here."

Mr Marshall, who will gather his members on Monday for a large meeting to discuss the new appointment, indicated the new chief officer might have a challenge on his hands, with the union leader telling his members that Mr Stephens was bad news for Melbourne firefighters.

“The UFU has serious concerns about the appropriateness of the appointment as we do not want to import the British fire services culture of forfeiting safe working conditions and firefighter positions for pecuniary purposes,” the union leader wrote in his bulletin.

Mr Marshall earlier had a clear warning to the Andrews’ government that there was trouble coming if it persisted with hiring Mr Stephens.

“We are surprised that a Labor Andrews government would support the appointment of Mr Stephens who has reportedly been party to union-busting tactics,” Mr Marshall wrote.

“This is a low point for union relations with the Andrews government and will be a defining moment in the short and long-term relationship.”

But Mr Merlino said Mr Stephens had been a fighter for the rights of the workforce on the Mersey brigade.

“Mr Stephens is ... a strong advocate for the rights of firefighters, improving the safety of the community and fighting against government budget cuts in his role at the helm of the Merseyside Fire Rescue Service," the minister said.

“We have always been determined that a wide-ranging search would be undertaken to find the best possible candidate for this important role.

"A key part of Mr Stephen's role will be to rebuild the relationship between management and the MFB workforce."