CANBERRA, Australia - Australia's prime minister said Monday that he was confident that government lawmakers would win a court challenge this week that threatens his administration's slender majority.

Seven High Court judges will decide whether seven lawmakers should be disqualified from Parliament because of a constitutional ban on dual citizens being elected. The three-day hearing begins Tuesday.

The fate of Deputy Prime Minister Barnaby Joyce is most crucial to the government in an unprecedented political crisis.

If the court rules that he was illegally elected in July last year 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.

Joyce could stand in a byelection, having renounced his Kiwi citizenship. But with the government unpopular in opinion polls, voters in his rural electoral division could take the opportunity to throw both the deputy prime minister and his administration out of office.

Two of the six senators under a cloud are government ministers. Fiona Nash inherited British citizenship from her father and Matt Canavan became an Italian through an Australian-born mother with Italian parents. Disqualified senators can be replaced by members of the same party without need for an election.

Prime Minister Malcolm Turnbull has given no indication of what his government would do if the court rules against any of the three ministers.

"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.

But several constitutional lawyers are less confident that the government lawmakers will survive the court scrutiny. Decisions made by illegally elected ministers could also face court challenges, although laws passed by the votes of ineligible lawmakers would not be changed.

"The courts have been pretty strict about this in the past and certainly haven't been terribly sympathetic to the 'I didn't know' argument," Sydney University constitutional lawyer Anne Twomey said.

"Given that they're confronted with so many people who seem to have the problem, maybe they'll think that they need to do something about it, who knows?" she added.

Public attention has focused on lawmakers' eligibility since July 14, when Scott Ludlam, the then-deputy leader of the minor Greens party, revealed he was still a Kiwi and had been unlawfully elected to the Australian Senate three times since 2007. The other six lawmakers soon discovered they were also dual nationals.

Three parliamentary investigations recommended in the 1980s and 1990s that the prohibition on dual citizens be removed from the constitution through a national referendum.

But successive governments have failed to act, perhaps because of the difficulty in persuading Australians to change their constitution. Of the 44 referendums Australia has held since 1901, only eight have been carried, and none since 1977.

George Williams, Dean of Law at the University of New South Wales, said the dual citizen ban effectively allowed the citizenship laws of other countries to determine who could stand for the Australian Parliament.

"We are really an odd one out here because in other nations it's commonly recognized that of course you can be a citizen of a different country so long as you're also a citizen of the country where you're standing for parliament, and that's because dual citizenship is so common," Williams said.

News from © The Associated Press, 2017