Enquiries by Australian media - not the New Zealand Labour Party - led to Internal Affairs discovering Australian Deputy Prime Minister Barnaby Joyce is 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.
The deputy prime minister said yesterday he was "shocked" to have been told he may be a New Zealand citizen by descent.
Mr Joyce told the Australian Parliament he was alerted to the situation after enquiries were made by the New Zealand Labour Party to the New Zealand government.
But Internal Affairs Minister Peter Dunne said Australian media had asked the department about Mr Joyce before Labour MP Chris Hipkins filed written questions on citizenship.
Mr Hipkins asked the government whether children born in Australia with a New Zealand father were citizens.
He told RNZ he asked about the rules for citizenship after discussions with the Australian Labor Party last week, but said they never discussed Mr Joyce specifically.
Mr Hipkins said he wouldn't have asked the questions had he realised how the issue would unfold this week, saying he had no interest in getting involved in Australian domestic politics.
Speaking to Morning Report today, Labour leader Jacinda Ardern said the party was not looking to make a formal complaint over Mr Joyce's comments, but it had been made very clear that Labour was not involved in the information that was passed on.
"We weren't involved in that and I don't know why Mr Joyce has named us in that way.
"But it's for Mr Joyce to manage the situation, we're not too fussed about the fact that he's incorrectly named us. I imagine he's got a lot of things on his mind, as anyone would in these circumstances. So for us, making sure the record was straight was important, but we're not going to be making anything formal to make sure the record is clear."
Dr Anna Hood, who lectures in immigration and international law at Auckland University, said it would be "relatively straightforward" for Mr Joyce to renounce New Zealand citizenship.
The law in New Zealand was that if someone's parent was a New Zealander, they became a New Zealand citizen.
But under the rules anyone over 18, of sound mind and holding citizenship of another country, could make a declaration of renunciation to the Internal Affairs Minister in New Zealand.
"The minister does have some discretion as to whether your declaration is accepted but I suspect in Barnaby Joyce's case it will be relatively straightforward for him."
'We were all British subjects at that time'
Australia's National Party leader was born in Tamworth in New South Wales in 1967.
Mr Joyce 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.
Mr Joyce said the Solicitor-General had advised that he would not be disqualified by section 44 of the constitution but 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 - stepped down after conceding they were dual citizens.
- ABC / RNZ