The High Court is double-checking the eligibility of the Liberal candidate who was due to fill the NSW Senate seat vacated by former cabinet minister Fiona Nash.
It is yet another twist in the citizenship saga engulfing federal parliament.
As three new senators were confirmed by the court, an affidavit was filed on behalf of NSW Liberal Senate candidate Hollie Hughes raising the issue of the timing of her accepting and resigning from a job with the Administrative Appeals Tribunal.
Under the constitution, holding an "office of profit under the crown" disqualifies a person from being a member of parliament.
Ms Hughes' legal counsel Arthur Moses told the court on Friday it was important to test her eligibility under the constitution to ensure "transparency".
"She will contend she is the person who should be declared duly elected to the Senate," Mr Moses said.
"The reason why the affidavit was filed ... on her behalf was to be completely transparent with the court as to the factual issues - to ensure this does not become a festering sore down the track."
Ms Hughes will be asking the government to cover her legal costs.
Liberal Hollie Hughes's eligibility for the Senate has been questioned. Source: NSW Liberals Facebook
The full court will hear the matter on Wednesday, two days after replacements are sworn in for Malcolm Roberts, Larissa Waters and Scott Ludlam who were ruled ineligible to sit in parliament because of their dual citizenship status.
Business consultant Fraser Anning will step into the Queensland One Nation seat vacated by Mr Roberts.
And 23-year-old student Jordon Steele-John will replace Mr Ludlam as Greens senator for Western Australia.
An affidavit was filed with the court on Friday in regard to former Australian Democrats leader Andrew Bartlett who will replace Ms Waters as Greens senator for Queensland.
There have been questions raised in the media about whether Mr Bartlett's university post could disqualify him.
However, Justice Stephen Gageler described it as "hearsay material" and he was satisfied Mr Bartlett had been duly elected.
The three confirmed senators will be sworn in on Monday ahead of the Senate voting on a new president to replace Liberal Stephen Parry, who resigned over his dual citizenship.
The position is tipped to go to Special Minister of State Scott Ryan.
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From Vietnam, where he is attending the APEC summit, Mr Turnbull has threatened to use the government's slim majority in the lower house to refer to the High Court any MP whose eligibility to sit in parliament is in doubt because of their dual citizenship status.
That's brought an angry response from Labor, which faces the prospect of four of its MPs - Justine Keay, Madeleine King, Susan Lamb and Josh Wilson - being disqualified from parliament.
Opposition Senate leader Penny Wong accused Mr Turnbull of behaving like a "tin- pot dictator".
"This is really a very desperate and diminished prime minister we've seen," she told 5AA radio in Adelaide on Friday.
Greens leader Richard Di Natalie told Sky News a "slightly unhinged" prime minister was losing the plot ,and the minor party was considering petitioning the governor-general to dissolve parliament and call a general election, he said.
Mr Turnbull, speaking to reporters in Da Nang, refused to say whether he had discussed the government's stability with Sir Peter Cosgrove.
"I never comment on discussions with the governor-general," he said.
Nor would the prime minister speculate on what number of by-elections would be too many.
Before leaving Australia, Mr Turnbull told independent MP Rebekha Sharkie she may have to refer herself to the High Court over the timing of her renunciation of British citizenship before the 2016 election.
On the government side, there are reports Liberal backbencher John Alexander could quit his Sydney seat as early as this weekend because he believes he is a British citizen by descent.
Ms Keay has admitted she waited three months before following the advice of Labor Party officials and renouncing her British citizenship after the 2016 election was called.
She acknowledged the only way to determine her eligibility was to have it tested in the High Court.
"Part of me sort of thinks - that probably is the only step to really put an end to all this and completely clarify it," she said.
Mr Turnbull is in Asia until next Wednesday after being unable to broker a deal with Mr Shorten over a citizenship disclosure scheme.
The prime minister dismissed Mr Shorten's request not to make partisan referrals to the High Court as "unworthy", saying the coalition had earlier referred its own MPs despite advice they were in the clear.
Mr Turnbull has proposed December 7 - the final scheduled sitting day of parliament for the year - as the deadline for MPs to lodge their documents.
That would rule out any High Court referrals until the parliament next sat, either on a sitting day added to the 2017 calendar or February 5 when it's scheduled to resume in 2018.
Labor wants a December 1 deadline.
