The Australian High Court today begins hearings into whether seven federal politicians, including the Deputy Prime Minister, meet the citizenship rules allowing them to run for Parliament.
Some have New Zealand connections.
The court's decision - expected within weeks - could result in a string of disqualifications, and further chaos for the Turnbull government.
Deputy Prime Minister Barnaby Joyce revealed to Parliament in August his father was born in New Zealand.
Despite emigrating to Australia before his son was born, New Zealand law made Mr Joyce a Kiwi by descent.
He has since renounced his New Zealand credentials.
Matt Canavan resigned from the Turnbull ministry when he discovered he may have been an Italian citizen by descent, through his Italian-born grandparents.
Fiona Nash, Deputy Nationals Leader, learnt she was a UK citizen by descent, because her estranged father was born in Scotland.
She argued she did not know, because she'd had minimal contact with her dad growing up - but she did understand her sisters, who were born in the UK, were dual nationals.
The High Court has already ruled One Nation party member and Senate crossbencher Malcolm Roberts was still a British citizen at the time of the 2016 federal election, after being born in India to a Welsh father and an Australian mother.
The former Greens senators Scott Ludlam and Larissa Waters have already left their seats and south Australian crossbencher Nick Xenophon has signalled plans to quit to run in next year's state election.
Those fighting the case are urging the Court of Disputed Returns not to take a literal view of the constitution.
The Commonwealth will argue those who took reasonable steps to renounce any foreign citizenship as soon as they were aware should not be disqualified and that all bar One Nation's Malcolm Roberts and the Greens Scott Ludlam remain eligible.