Victoria's Acting Premier Jacinta Allan says two Liberal MPs betrayed the Parliament and their faith by returning to vote after asking to be excused on Good Friday.

Key points: Craig Ondarchie and Bernie Finn asked to be excused on religious grounds on Good Friday but then returned to vote

Craig Ondarchie and Bernie Finn asked to be excused on religious grounds on Good Friday but then returned to vote Government said the MPs' actions were an "absolute disgrace"

Government said the MPs' actions were an "absolute disgrace" Opposition says Government tried to use sick MP's absence to push through bill

The Government's bill to divide the fire services and grant presumptive rights to firefighters with cancer was shockingly voted down after a marathon sitting of the Parliament, when two Liberal MPs who had asked to be excused on Good Friday unexpectedly returned to vote.

Liberal MPs Bernie Finn and Craig Ondarchie have not returned calls for comment.

The duo were excused from the debate under a practice called pairing, where an MP who is absent requests an MP from the other side to also excuse themselves so the numbers are unchanged.

Ms Allan said their actions were a betrayal of the Parliament and their religion.

"The Liberal Party and certainly [Opposition Leader] Matthew Guy have absolutely forfeited their right to lecture anyone ever again on issues to do with honesty, integrity or probity," she said.

"What we saw happen on the morning of Good Friday, the betrayal on Good Friday of not just the institution of the Parliament but also religious institutions as well, was an absolute disgrace."

Victorian Greens MP Nina Springle was emotional after the fire services bill was defeated. ( ABC News )

Ms Allan said there would have to be discussions about pairing arrangements in the future.

"It's hard to find an example in any parliament around the country that this has happened ever before," she said.

"It's a fundamental betrayal of the Parliament, of how parliament works, of how Members of Parliament respect each other and respect, whether it's their private beliefs, or respect the fact that they may need from time-to-time go and be with a sick relative go and care for other people."

She said Mr Guy needed to front up and explain who devised the plan.

"Matthew Guy and his Liberal-National coalition colleagues should be fronting up and explaining why they did it, whose call was it," she said.

"This leadership call that we're hearing, whose call was it? They just cannot be trusted on anything they say or do ever again."

Labor MP Jaclyn Symes said the breach of pair conventions on Good Friday was "shameful". ( ABC News )

Government 'preyed' on sick MP's absence: Opposition

Mr Guy tweeted on Saturday that he was proud of his colleagues, but has not faced the media.

An Opposition spokeswoman said comments made on Friday by shadow attorney-general John Pesutto still stand.

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Liberal MP Tim Smith said the Government forced the Parliament to sit on Good Friday because it wanted to ram through the CFA changes while crossbench MP Rachel Carling-Jenkins was off sick.

Dr Carling-Jenkins was absent from Parliament on Wednesday and Thursday last week, but the Government said she did not ask for a pair.

Mr Smith said the Government preyed on her absence, as she was known to oppose the bill.

"Labor cynically took an opportunity to try and ram it through on Good Friday, and only the Liberal and National Party stood up for the CFA," he said.

He rejected the suggestion Mr Finn and Mr Ondarchie had used God as an excuse for a political manoeuvre.

"The Liberal and National Party gave an undertaking to protect those who protect us, that's the CFA, and the Labor party cynically used the absence of a sick MP to try and ram through a bill," Mr Smith said.

"Where if they'd simply waited 'til April, the Parliament would have reflected its true numbers and the bill would have been voted down again.