The return of former Democrats leader Andrew Bartlett to the Senate could be short-lived, with the Greens at risk of losing a third senator to the same section of the constitution that claimed Larissa Waters and Scott Ludlam.
Mr Bartlett, whose path back to parliament as a Green opened up after Ms Waters fell foul of section 44 of the constitution, could be blocked by a subsection that forbids candidates from holding an "office of profit", as he was working for a university at the time of his nomination.
Ms Waters, born in Canada, and Scott Ludlam, born in New Zealand, both resigned in the past week after discovering they held dual-citizenship, which is not allowed under section 44 of the constitution.
The former Democrat senator was second on the Queensland Greens ticket and is expected to take Ms Waters' place in a recount.
Constitutional law expert and dean of law at the University of New South Wales, George Williams, said university employment was a "grey zone", and carried a risk the High Court would rule it a breach of the constitution.
"There is no doubt there is a risk," he said.
"It is not clear what the answer would be. It is possible it is covered and it is possible it is not.
"But it is yet another reason which shows why this provision needs reforming."
Mr Bartlett said he believed he was in the clear despite working as a research fellow with the Australian National University at the time of his nomination.
"It is not correct to assert that a university position is an office of profit under section 44," he said.
"We've had strong advice to the contrary for some years and people have been elected to parliament previously without resigning their university position."
It has never been tested in the High Court whether a university position could count as holding "any office of profit under the Crown", though section 44 has previously stopped public servants, including teachers, from running for parliament.
In 1992, Phil Cleary, who won the seat of Wills in a byelection as an independent, was found to have been ineligible by the High Court, despite having taken leave without pay from his teaching job.
The Greens have defended their process in nominating Mr Bartlett by citing advice from the National Tertiary Education Union, which points out there has not yet been any legal challenges of university staff elected to federal parliament and states that the weight of opinion is they are not considered part of "the Crown".
However, it is understood that the major political parties insist that candidates who hold university positions resign ahead of their nomination to the Australian Electoral Commission.
Greens leader Richard Di Natale said on Tuesday that his party will conduct a review into its party processes following the resignations.
"We are committed to a thorough root and branch review so that we strengthen our governance, improve our internal processes and we make sure that this never happens again," he said.
Senator Di Natale and his Tasmanian senator Nick McKim are both waiting on documentation to prove they renounced their Italian and English citizenships, after Ms Waters and Mr Ludlam's revelations sent foreign-born MPs from all parties scrambling to prove their status as sole-citizens.
Senator Di Natale says he renounced his second citizenship before entering the Australian Parliament a decade ago, although Senator McKim has admitted he previously served in the Tasmanian parliament as a dual-citizen.
A spokewoman for Senator Di Natale said he will receive official documentary evidence early next week. Senator McKim has requested confirmation from the UK Home Office but it is not currently known when this will be received.
The Greens are expecting the government to follow convention and waive the repayment of the $3 million in salaries Mr Ludlam and Ms Waters earned during their time in the senate, following in the footsteps of an agreement offered to Family First senator Bob Day.
The 45th Parliament has so far lost four senators to section 44 of the constitution.
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