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 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.
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.
