What the citizenship rulings mean

HOW DOES THIS AFFECT THE GOVERNMENT?

The Turnbull government's one-seat majority is under threat, although the prime minister insists it's business as usual.

Although Barnaby Joyce is expected to win the December 2 New England by-election, the disqualified deputy prime minister won't return to parliament until February at the earliest, so the government must negotiate two sitting weeks without him.

Until then, it will rely on the vote of at least one crossbencher to retain the confidence of parliament and pass legislation through the lower house.

Independent Cathy McGowan has indicated she will support the government against any vote of no-confidence and for supply.

LABOR'S RESPONSE

Deputy leader Tanya Plibersek says the party isn't planning any "mischief" in parliament. But she gave a strong indication the opposition will exploit the government's fragile position to revisit cuts to penalty rates and a banking royal commission, both issues which the government won by one vote.

They will also rely on crossbenchers.

BARNABY JOYCE

Ruled to be "a subject or a citizen ... of a foreign power" at the 2016 federal election and therefore disqualified from parliament.

Despite being born in Australia, the Nationals leader inherited dual New Zealand citizenship from his father who moved to Australia long before Joyce was born.

Joyce will contest a by-election in his seat of New England on December 2 and is favoured to win, while arch rival Tony Windsor has said he will not run.

"In my gut I thought this is the way it was going to go," Joyce said.

Prime minister Malcolm Turnbull will take over his portfolio of agriculture minister until the by-election.

Nigel Scullion will become interim Nationals leader.

FIONA NASH

The Nationals' deputy leader was also ruled ineligible due to her British citizenship because her father was born in Scotland.

Her Senate seat is likely to go to the next person on the NSW coalition ticket, Liberal Hollie Hughes which would alter the balance in the coalition.

Nash's portfolio of regional communications will go to Senator Mitch Fifield and Darren Chester will take over regional development and local government.

MATT CANAVAN

The Queensland Nationals senator was ruled not be ineligible after his lawyer successfully argued against his Italian dual citizenship.

In one bright spot for the government, Canavan had stood down from the Senate but will be restored and resume his job as resources minister.

SCOTT LUDLAM

The WA Greens senator was ruled ineligible because he was a dual citizen with New Zealand.

He had already resigned his seat which will be taken by the next candidate on the West Australian Greens ticket, 23-year-old student Jordon Steele-John. Ludlam says he has no interest in politics in the short or medium term.

MALCOLM ROBERTS

The One Nation senator from Queensland was ruled ineligible after already being declared a British citizen by the High Court because he was born to a Welsh father in India.

Roberts will run for the seat of Ipswich in the Queensland state election.

"I accept the decision entirely. I'm disappointed to be leaving federal parliament but that opens another door."

He is likely to be replaced by Fraser Anning.

LARISSA WATERS

Born in Canada to Australian parents, Waters came to Australia as a baby but was ruled ineligible as she still held Canadian citizenship.

The former Queensland Greens senator also stood down but says she will run for preselection for the next federal election.

She will be replaced by the next person on the Queensland Greens ticket, former Democrats senator Andrew Bartlett.

"I'm personally disappointed but I'm not surprised," she said.

NICK XENOPHON

Xenophon was ruled to be eligible because he only had a subclass of British citizenship through his father who was born in Cyprus.

But Xenophon is quitting federal parliament to run in the next South Australian state election.

He will be replaced by the next person on the NXT ticket, business consultant Tim Storer.