Deputy prime minister Barnaby Joyce became the most high-profile politician to be embroiled in the scandal when news surfaced on Monday the Nationals leader is a New Zealand citizen.
Mr Joyce revealed in parliament yesterday he had been advised by the New Zealand high commission he could be a New Zealander as his father was born there.
New Zealand Minister of Internal Affairs Peter Dunne said that under the 1948 New Zealand Citizenship Act, every person born outside of New Zealand to a parent who was a New Zealand citizen by birth was automatically a New Zealand citizen.
He refused calls to resign, even though two Greens MPs resigned last month after learning they were dual citizens.
MALCOLM Turnbull is facing the real possibility that he will be forced to seek an alliance with a crossbench MP to hold onto government.
Mr Shorten declined, saying all Labor MPs were properly vetted before running for parliament. Joyce was born in Australia in 1967.
However, Mr Hipkins insisted his friend did not ask him to lodge the question, he had no idea it was related to Mr Joyce, and he was just interested in the topic.
"We did not refer this matter to the court because of any doubt about the Member for New England's (Joyce's) position, but because of the need, plainly in the public interest, to give the court the opportunity to clarify the operation of the section (of the constitution) so important to the operation of our Parliament", Turnbull told Parliament.
Australia and New Zealand haven't seen a row quite like it since Trevor Chappell bowled underarm to New Zealand batsman Brian McKechnie in 1981. Ludlam was born in New Zealand and Waters was born in Canada.
The development follows an unusual saga in recent weeks with queries raised about numerous Australian MPs after it emerged that some may unwittingly be citizens of foreign countries.
Labor leader Bill Shorten used question time to pressure the prime minister over his reluctance to stand Mr Joyce aside, and is expected to ramp up the attack today.
Labor's Tony Burke said the party was confident it did not have any dual citizens among its ranks, thanks to its detailed and "cumbersome" process for vetting the status of candidates.
"He's been very clear: Yes, someone from the ALP put some legal question to him around citizenship, no mention was made of anyone's name, no rationale for any particular case being pursued was ever raised".
That prompted Mr Turnbull to ramp up the rhetoric against Labor over the citizenship saga.
Attorney-General George Brandis said the situation involving Queensland senator Matt Canavan - who stood aside from cabinet last month and has decided not to vote in the chamber until his Italian citizenship issue is resolved - was different to that of Mr Joyce.