Experts have cast doubts on the parliamentary future of stood-aside minister Matt Canavan, while another senator is facing mounting pressure over dual citizenship.
Senator Canavan, a Queensland Liberal National Party senator, resigned from the frontbench on Tuesday after discovering his mother made him a dual Italian citizen 11 years ago.
He was 25 at the time and did not sign the form, but had taken part in a family discussion about it in 2005.
Under Section 44 of the constitution, a person is disqualified from being elected if at the time of their election they are a citizen of "a foreign power" or otherwise have an "allegiance, obedience or adherence to a foreign power".
The Senate will refer the matter to the High Court on August 8, which could lead to Senator Canavan losing his seat.
The government has preliminary legal advice that because the registration was obtained without Senator Canavan's knowledge or consent he is not in breach of Section 44.
However, a senior immigration lawyer told AAP the court did not appear to have any flexibility in the Canavan case, as his mother's application met the proper requirements for citizenship under Italian law.
"I can't see there's suddenly any flexibility or discretion to create a consent because no one consents to citizenship," the lawyer said.
"Canavan can argue the need for consent but I can't see the High Court inventing that under Section 44."
Senator Canavan, who was promoted to cabinet last year after two years in parliament, will still serve as a senator while the court decides his fate.
Meanwhile, fresh questions have arisen over the dual citizenship of One Nation senator Malcolm Roberts, who was born in India to a Welsh father.
Documents obtained by Buzzfeed News show Senator Roberts' name in a UK High Commission birth index which notes his Indian birthplace.
He is also listed as having travelled by ship on a British passport with his parents when he was a young child.
Senator Roberts, who is seeking an inquiry into citizenship following the resignations of two Greens senators, says prior to running for One Nation in 2016 he "fully investigated" whether he was eligible to sit in parliament.
He uploaded to Twitter a statutory declaration detailing his investigation.
"I can confirm I am not a citizen of the United Kingdom, nor am I a citizen of India. I am a citizen of Australia only."
But Senator Roberts has declined to release documents relating to his renunciation, including its timing.
Defence Minister Marise Payne encouraged Senator Roberts and any other MPs facing citizenship questions to provide evidence to "shine a light" on their positions.
"I would have thought that the greater light that is shone, the greater clarity that is available, the better," Senator Payne told ABC radio.
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