New Zealand Internal Affairs Minister Peter Dunne has confirmed Australian Deputy Prime Minister Barnaby Joyce is considered a New Zealand citizen.
Mr Joyce is the latest politician to be caught in a dual citizenship controversy across the Tasman.
Several senators have resigned, or are facing scrutiny, over their citizenship status.
Under the Australian constitution, anyone with dual citizenship cannot stand for federal election.
Mr Dunne said Mr Joyce's father was a New Zealand citizen and he passed citizenship on to his son.
"It's automatically passed on, I don't know whether he (Mr Joyce) knew or not," Mr Dunne said.
"He says he didn't know, he says he was under the belief his father had renounced the New Zealand citizenship.
"But the fact is it is all irrelevant - if he was eligible to receive the citizenship at the time, under our legislation he does, regardless of his subsequent circumstances," Mr Dunne said.
Mr Joyce said this afternoon he was asking the High Court to rule on his citizenship status and whether he was eligible to be in Parliament, the ABC reported.
He said legal advice suggested he has not breached the constitution, but the court should consider the matter.
Mr Joyce told Parliament the New Zealand High Commission contacted him last Thursday to say he might be a citizen of New Zealand because his father was born there.
"The New Zealand High Commission contacted me to advise that on the basis of preliminary advice from their Department of Internal Affairs, which had received inquiries from the New Zealand Labour Party, they considered that I might be a citizen by descent of New Zealand."
He said he was "shocked" to hear the news.
"I have always been an Australian citizen," he said.
The National Party leader was born in Tamworth in New South Wales in 1967.
He said his father was born in New Zealand but moved to Australia in 1947 "as a British subject - in fact we were all British subjects at that time".
He noted that the concept of New Zealand and Australian citizenship was not created until 1948.
"Neither my parents nor I have ever applied to register me as a New Zealand citizen, the New Zealand Government has no register recognising me as an New Zealand citizen," he said.
Mr Joyce said the Solicitor-General had advised that he would not be disqualified by section 44 of the constitution.
But he said that he was asking the High Court to make a ruling to clarify the situation.
Prime Minister Malcolm Turnbull said Mr Joyce should remain as deputy prime minister because the legal advice was so strong.
Last week the Senate referred four cases to the High Court to decide on eligibility.
National Party senator Matt Canavan and One Nation senator Malcolm Roberts will both argue in the High Court that they should not be disqualified as dual citizens.
Two Greens senators - Scott Ludlam and Larissa Waters - have both quit after conceding they are dual citizens.
kia ora barnaby— Scott Ludlam (@Scottludlam) August 14, 2017
The High Court will make a ruling about the process for replacing the two Greens.
A spokesperson for New Zealand's Labour Party said they did not have a comment to make at this time.
- ABC / RNZ