Prime Minister Scott Morrison is facing a rebellion on the floor of Parliament, with Coalition MP Llew O’Brien threatening to cross the floor and vote with Labor to legislate for an anti-corruption watchdog.

The potential defection represents the biggest threat to the Morrison government’s control of Parliament since Malcom Turnbull was forced to legislate a royal commission into the banking sector.

Parliament resumes on Monday for the first time since the Wentworth by-election delivered a parliamentary minority.

Kerryn Phelps’ win in Mr Turnbull’s vacated Sydney seat means the Coalition is forced to rely on the support of one of the six crossbench independents to pass legislation.

The Queensland MP’s vote would deliver Labor and the independents a majority – 75 votes – but Labor will still need another Coalition MP to defect or independent Bob Katter to support the corruption watchdog to deliver an absolute majority of 76 votes to bring on a debate in Parliament.

A former police officer who joined the force in the post-Fitzgerald inquiry period, Mr O’Brien told The New Daily that he believed an integrity commission was an important measure to restore public trust in the political system.

The Member for Wide Bay in Central Queensland confirmed he will hold talks with Attorney-General Christian Porter on Monday.

“I think it’s a bit of a no-brainer at the federal level,” Mr O’Brien told The New Daily.

“It has the potential to serve a very important purpose and it meets community expectations.

“Much of the public have lost trust in the political system and politicians and this is certainly a step in the right direction of rebuilding that trust.”

It is a rare occurrence for Labor and the crossbench to be able to legislate from the opposition benches and would require an absolute majority to force the government to debate the legislation.

There is already speculation Victorian Liberal MP Julia Banks could supply that vote.

While Mr O’Brien stopped short of pledging to cross the floor, he confirmed he would also hold talks on Monday with crossbench independent Cathy McGowan.

“All I will say is this is a matter I have given much consideration to and as it stands I am not ruling out supporting an appropriate bill,” he said.

Labor leader Bill Shorten flagged his intention to seek the support of the crossbench to legislate for a national integrity commission.

“We will work with the Coalition, but we will not wait for them,” Mr Shorten said.

SA Independent Rebekha Sharkie told The New Daily she saw the commission as the biggest reform since the banking royal commission and was vital to restoring public trust.

“Nobody should be above the law,” she said.

On Sunday, Mr Porter left open the door to new measures to strengthen the “integrity regime” in response to an open letter from 34 former judges urging the government to act.

“Governments ignore at their peril demands by citizens to combat corruption with vigour,” the letter states.

In response, Mr Porter said the model proposed would “apply extraordinary powers against all public servants, including ABC and SBS journalists”.

“Those powers could be used without proper checks and balances and at large because of an incredibly broad and low definition of corruption including basic administrative errors and process failures by public servants,” Mr Porter said.

“But (the judges) do not appear to support the same integrity commission extending to cover the judiciary. While the government has been working on, and is open minded to what may be the best way to improve our present multi-agency integrity regime, the model proposed by the crossbench may be useful to generate debate. But it would not be a workable path forward in practice.”