Victoria's anti-corruption watchdog will be asked to investigate claims of union blackmail and secret deals by the government in the lead up to the 2014 election.
Opposition leader Matthew Guy said he would be writing to IBAC to request an investigation into Labor government negotiations with the United Firefighters Union prior to the poll.
He has claimed the government made a deal with union boss Peter Marshall in exchange for the union's endorsement at the election.
Mr Marshall on Wednesday said a deal had been struck and threatened to reveal the details before the November state election.
"We are pretty concerned about this, I've never seen anything like it before where a union leader is holding the government to ransom and the government is pretty cagey with their answers," Mr Guy told reporters on Friday.
Both the Premier and Emergency Services Minister James Merlino denied entering a secret deal with the union.
Any pre-election pledges about fire services were above board, deputy premier Mr Merlino said on Friday.
"There is nothing the opposition says on this matter that can be trusted," he added.
"We've had decades of conflict between management and its workforce and that's a reflection of everyone.
"Everyone needs to look in the mirror in terms of the roles that they've played in fire services over many decades."
The premier said it was inappropriate to comment on the workings of IBAC but labelled Mr Guy "completely irrelevant".
Mr Marshall's furious interview followed the appointment this week of British fire chief Dan Stephens as the new boss of the Metropolitan Fire Brigade.
