Australia's highest court has begun a three-day hearing to decide whether lawmakers with dual citizenship are eligible to sit in parliament.
Australia's parliament was rocked by revelations in August that the seven politicians, including the deputy prime minister and two other Cabinet members in Prime Minister Malcolm Turnbull's coalition government, are dual citizens.
"The government, based on the legal advice we have from the solicitor-general, is confident that the (deputy prime minister) and the other two senators, Nash and Canavan, will be found not to be disqualified from sitting in the Parliament", Turnbull told reporters.
Those parliamentarians who "can honestly swear to being unaware" should be taken at their word, the government argued.
Solicitor-general Stephen Donaghue said: "If a person is not aware either that they are a dual citizen or of a significant prospect that they are, in our submission by definition that person can not have a split allegiance".
The cases involve Mr Joyce and his government colleagues Fiona Nash and Matt Canavan, as well as four politicians from minor parties - Malcolm Roberts, Nick Xenophon, Larissa Waters and Scott Ludlam.
Barnaby Joyce, whose citizenship is under question, will be acting Prime Minister this week.
Prime Minister Malcolm Turnbull has given no indication of what his government would do if the court rules against any of the three ministers.
It was only when a law passed in 1983 that the citizenship status of Senator Canavan was changed without his knowledge, in what he said was a "critical quirk" in the Queensland senator's case.
The High Court hearings are another setback for a government that continues to struggle in the polls.
If the court rules that he was illegally elected in July a year ago due to New Zealand citizenship he unknowingly inherited from his father, the ruling conservative coalition could lose its single-seat majority in the House of Representatives, where governments are formed.
We'll get to that - and to the former New England MP Tony Windsor, who is challenging Joyce's eligibility, over the coming days.
David Bennett QC said various changes to Italian law had led to the situation now before the court, and his client should not be punished by being kicked out of parliament.
Senator Xenophon announced on Friday that he would quit the Senate to seek a seat in South Australia's lower house, meaning he will be replaced regardless of the court's decision.
Those fighting the case are urging the Court of Disputed Returns not to take a literal view of the constitution.
Senator Roberts is expected to be ruled ineligible by the court, with One Nation candidate Fraser Anning expected to take his place.
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