Questions over the eligibility of a second crossbench senator have plunged the nation's upper house into chaos and forced the federal government to refer both cases to the High Court for adjudication.
Just a day after the government said it would test Bob Day's eligibility in the High Court, Attorney-General George Brandis revealed that a private case being brought against One Nation's rookie WA senator Rod Culleton had raised the question of whether he was capable of being elected.
That led to advice being sought from the outgoing Solicitor-General, Justin Gleeson, which supported Senator Culleton's eligibility being tested in the High Court.
The explosive developments have added extra uncertainty to the Turnbull government's numbers, putting the opposition within a pair of crossbench votes of being able to block crucial legislation for the remainder of the year.
The High Court will be asked to decide if now-resigned Family First senator Mr Day was eligible to stand in July, and will now also rule on the fitness to stand of Senator Culleton, over a criminal conviction recorded against him at the time of the election.
As Mr Brandis revealed the second case, Fairfax Media reported that Mr Day's unorthodox office arrangements since 2014 – the cause of doubts over his eligibility – had initially been approved by the Abbott government in 2014, against departmental advice.
The Finance Department had warned against the perception of a conflict of interest. "I recommend that you agree to not approve the establishment of a new electorate office for Senator-elect Day," its entitlements manager advised the then special minister of state, Michael Ronaldson, in a February 2014 letter.
Now those same arrangements are at the centre of advice to the government from an eminent QC, David Jackson, that Mr Day had a "indirect pecuniary interest".
"I've got no knowledge at all of what the Finance Department may have done in 2014," Senator Brandis told ABC's 7.30 on Wednesday night, adding that he first received advice on the potential constitutional breach on Thursday night.
When asked why the special minister of state only sought constitutional advice more than eight months after a lease was signed on Mr Day's office in December, he cited the change in ministers after the election.
"I can't tell you what passed between [outgoing special minister of state] former Senator Ronaldson and his department," he said.
The government's legislative ambitions for the final weeks of 2016, including its union-busting Australian Building and Construction Commission bill, and billions in welfare savings, are now being reconsidered amid growing fears of defeat.
A decision on whether to proceed with the ABCC bill next week is likely to be taken within the government on Thursday.
The Attorney-General said on Wednesday afternoon he had written to Senate President Stephen Parry on Saturday and drawn his attention to a legal opinion he had received from Mr Gleeson on Senator Culleton's election.
Senator Brandis said he received the legal advice on Friday, which was also provided to Senator Culleton. The Attorney-General sought the advice because former Culleton associate Bruce Bell is challenging Senator Culleton's election in the High Court.
"It appears that the proceedings brought by Mr Bell are based on an allegation that, at the time of the last election, Senator Culleton had been convicted of an offence punishable by a sentence of imprisonment for one year or longer, and was therefore 'incapable of being chosen' as a senator under section 44(ii) of the constitution," he said.
In a shambolic doorstop press conference in Perth on Wednesday, Senator Culleton repeated an earlier suggestion that he might voluntarily stay out of key votes in the Senate while the matter was determined, but hinted also that he might not attend any case, and questioned the right of the nation's highest jurisdiction.
He said there was a "a very dark cloud" hanging over the High Court, even as he revealed his intention to represent himself when the case comes up.
But he also said: "I'm not sure I'll participate in any High Court jurisdiction."
He observed that "I'm not here to be cross-examined by the media", despite it being a press conference.
At another point, he described the constitution as the real law of Australia.
"This is a constitutional matter and boy am I sharp on the Constitution (the real law of Australia) so this is right up my veggie patch," he said.
The West Australian had a larceny conviction for stealing a car key annulled in court in August, but the annulment was after he was elected at the July 2 poll.
"A single action over a $7.50 [key] could now lead to an entire nation being stopped," he said.
Senator Culleton also cast doubt on the weight to be placed on the legal opinion provided to the government by Mr Gleeson.
"It's not fact, it's just an opinion," he said.
"At all material times I was innocent," he maintained, despite having pleaded guilty.
Meanwhile, an angry Mr Day rejected the government's interpretation that he had contravened the constitution via an indirect pecuniary interest created when he insisted on occupying office space in Adelaide in a building he once owned. The building had been sold to a company on what he called "vendor financing" – essentially a loan.
Labor called on the government to release all legal advice provided and to outline exactly when it first knew about Senator Day's constitutional problem.
With Rachel Olding