Why is NZ Labour poking into Australian politics?

News.com.au reports:

AUTHORITIES in New Zealand have confirmed that our Deputy Prime Minister Barnaby Joyce is indeed a citizen of their country.

It puts increased pressure on the Nationals leader to step aside, as the matter of his apparent dual citizenship is examined by the High Court.

The shocking revelation, which Mr Joyce made in Parliament this morning, puts Malcolm Turnbull’s majority government under threat.

New Zealand’s Internal Affairs Minister Peter Dunne has confirmed Mr Joyce is a New Zealand citizen under the Citizenship Act of 1948.

Mr Dunne told local reporters that Crown Law had checked the circumstances and confirmed Mr Joyce was a citizen.

Labor has responded angrily to My Joyce’s declaration that on the basis of legal advice, he would carry on as Deputy PM and continue to vote on legislation in Parliament.

Tony Burke, the Manager for Opposition Business, told Parliament Mr Joyce must step aside and not vote on legislation until the High Court had ruled on his eligibility to be elected.

The call comes as an overwhelming response to a News Corp Australia poll, participated in by several thousand people, shows Australians are split down the middle on the issue.

In an extraordinary admission today, Mr Joyce told the lower house he learnt last week that he could be a citizen of New Zealand by descent via his father.

“Last Thursday afternoon 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 Labor Party, they considered that I may be a citizen by descent of New Zealand,” Mr Joyce told Parliament.

So why is NZ Labour trying to depose the Deputy PM of Australia?

Seems bizarre that when someone was born in Australia and has never applied for citizenship elsewhere, they could be ineligible to be an Australian MP.