The High Court will decide if Labor senator Katy Gallagher is allowed to remain in parliament or if she'll become the next victim of the citizenship saga.
Lawyers for the former ACT chief minister will argue the original steps she took to give up her UK citizenship were sufficient, when her case comes before the full bench on Wednesday.
Senator Gallagher completed a declaration of renunciation on April 20, 2016 and the UK Home Office deducted a fee for registration on May 6 - 10 days before the issuing of writs for the federal election.
Her lawyers say the information she provided was "sufficient there and then" to meet British requirements to cease citizenship, but the UK Home Office asked her on July 20, weeks after the election, to provide originals of her father's birth certificate, her parents' marriage certificate and her own birth certificate.
But Solicitor-General Stephen Donaghue has suggested in a submission that argument's "striking for ignoring, almost entirely, the words of section 44(i)" of the constitution, which deals with dual citizenship.
He said that could allow a person to refuse to provide further information to a foreign office if requested, remain a foreign citizen but still not be disqualified from parliament.
The decision could have implications for other MPs who were still dual citizens but seeking renunciation when they nominated.
The government wants her fellow Labor MPs Justine Keay, Josh Wilson and Susan Lamb to have their citizenship matters referred to the High Court.
There are also calls for crossbencher Rebekha Sharkie and Liberals Julia Banks, Jason Falinski, Alex Hawke and Nola Marino to be referred.