Labor Senator Katy Gallagher faces an anxious wait as the High Court considers whether she should be allowed to remain in parliament.
Government lawyers have urged the court to find Senator Gallagher ineligible, arguing she left it too late to renounce her British citizenship before the 2016 election.
But her legal team insists she took all reasonable steps to sever her foreign ties, claiming it was "incredibly uncertain" how long a person should wait for British officials to approve the paperwork.
If Senator Gallagher is disqualified under section 44 of the constitution, a host of other MPs who were still dual citizens when they nominated will face mounting pressure to be referred to the High Court or resign.
Senator Gallagher submitted her renunciation application on April 20, 2016 and was charged the associated fee on May 6, some 10 days before election writs were issued.
Her lawyers told the full bench on Wednesday that she provided sufficient details, but the British Home Office requested further information on July 20, almost three weeks after the election.
However, Solicitor-General Stephen Donaghue said renunciation processing times ranged between 55 and 60 days and could take up to six months.
Senator Gallagher left just 41 days for hers, despite being preselected 12 months before the election.
Dr Donaghue also argued the documents Senator Gallagher initially provided were insufficient - a point vehemently opposed by the senator's legal team.
The High Court has reserved its decision.