Labor senator Katy Gallagher may face a referral to the High Court over her eligibility to sit in the parliament under the Constitution.
Paperwork reveals the ACT senator was still a British citizen, through descent from her UK-born father, when she nominated in the lead-up to the last election.
Section 44i of the Australian Constitution states dual citizens cannot serve in the parliament. The rule has already seen nine federal politicians forced to resign this year.
Senator Gallagher’s own documents, uploaded to a public disclosure of citizenship paperwork that was released to the public today, shows the British Home Office did not confirm her renunciation of her British citizenship until August 16 last year – around a month after nominations for the 2016 election closed.
Senator Gallagher said she did not intend to refer herself to the High Court, meaning the Turnbull government would have to get a majority of senators to agree to force the referral.
"Based on all the advice I have available to me I do not believe that I should refer myself to the Court of Disputed Returns," the senator wrote on her Facebook page.
"However ultimately that will be a matter for the Senate to determine."
Senator Gallagher is in a similar position to fellow Labor senator Justine Keay.
Both took steps to renounce their foreign dual citizenships before the deadline but did not hear back from the authorities until afterwards.
The Coalition is threatening to refer the Labor senators in question to the High Court.
That's despite Labor's confidence the senators concerned took "reasonable steps" to rid themselves of their foreign citizenships, which was established as a legitimate excuse in the 1992 High Court case Sykes v Cleary.
"The difference between the Labor people who Malcolm Turnbull and Christopher Pyne keep referring to and the people who have been knocked out is the difference between people who took reasonable steps on the Labor side and people who took no steps whatsoever on the Coalition side," Labor's Tony Burke said on Monday.
Constitutional expert George Williams said there was no categorical answer to whether Senator Gallagher was ineligible.
"Whenever renunciation is received after the close of nomination there is always the question have reasonable steps been taken, for which the High Court has not yet provided any guidance," Professor Williams told AAP.
Australian Conservatives leader Cory Bernardi revealed he held Irish citizenship but had lodged a form renouncing it in 2006, before he filled a Liberal Party casual vacancy in South Australia.
But he did not provide the Irish government's formal reply to his renunciation.
Senator Bernardi told AAP on Monday: "Lodgement of the form is sufficient."
Section 21 of the Irish Nationality and Citizenship Act 1956 provides the renunciation occurs "upon lodgement of the declaration".
Prof Williams said Senator Bernardi could fall into the same trap as former One Nation senator Malcolm Roberts, who tried to renounce his British citizenship via email to the wrong address, but did not receive the formal renunciation notification until too late.
"It's obviously not enough just to send information in, you need to be diligent in following it up as well," Prof William said.
The larger problem with the declaration process was no independent person had been put in place to scrutinise the information and determine what should be taken forward to court.
Coalition politicians including Barnaby Joyce, Fiona Nash and Stephen Parry were all kicked out of parliament for breaching Section 44i.
They did not take any steps to renounce their foreign citizenships because they maintain they were not aware they existed.
Former One Nation senator Malcolm Roberts claimed he took reasonable steps to rid himself of his UK citizenship, but the High Court hearing revealed he had sent renunciation documents to non-existant email addresses.
The citizenship declarations and documents of all federal senators were released on Monday. MPs in the House of Representatives will also have to provide their paperwork to a public register later this week.
- with AAP
