National leader Christopher Luxon has refused to release the specific modelling behind his party's election tax policy, which has come under scrutiny from experts.
When pressed, the party leader refused to agree to release National's specific modelling for calculating how much money it would get from taxing foreign house purchases.
Currently, non-citizens are not allowed to buy residential property in New Zealand after the Labour-led government introduced a ban on foreign buyers.
National has argued the ban should be lifted, and instead, foreign buyers would pay a 15% tax on house purchases over $2 million.
National's leader was questioned about the policy in an interview with TVNZ's Q+A.
Luxon said he was "extremely confident" about his party's numbers and emphasised National had already released a 30-page document about how the policy would work.
"What I'd also say to you is since we've made those announcements, there's been a number of experts and advisors into the public domain and said: 'Look, this is great'."
Q+A host Jack Tame challenged Luxon to explain how the figures held up: "How exactly will you sell $20 billion worth of property over four years?
"Will you commit to releasing the specific modelling that shows how you will sell $20 billion worth of property to foreigners over the next four years?"
The combination of the reduction in the brightline test, reintroduction of landlord tax breaks and a potential influx of foreign buyers.
He responded: "I'm not debating your numbers. I'm saying to you very clearly that we're going to make sure we deliver working New Zealanders income tax relief."
When pushed whether he would release the underlying modelling behind National's calculations, Luxon said: "We've already released the information we're going to release."
He later added: "We have released our reviewers who have gone through all our assumptions. I'm very comfortable with that."
Labour's finance spokesperson Grant Robertson has called the plan "voodoo economics", whilst experts have debated the potential risks of the plan on New Zealand's tax treaties.
University of Auckland law professor Craig Elliffe wrote on 1News.co.nz that there are significant risks the policy would spark either economic or diplomatic repercussions.
New Zealand has a range of agreements with other countries on tax, which sit alongside trade agreements, many of which include "non-discrimination" clauses so that overseas nationals cannot be taxed by the Government in ways New Zealanders would not be.
"We're confident that our modelling stacks up," the party's deputy leader and finance spokesperson said.
Luxon was also pushed on his housing policy, where he said National hadn't carried out any "specific modelling" for its effects on house prices.
The price of houses has soared in the past six years under the Labour Government.
"We have a housing problem in New Zealand. We have talked about this for years, this government under six years has actually made things worse, and it's been an absolute failure," he said.
"We are determined to make action on the housing market, and we've got to do three things at the same time."
Q+A with Jack Tame is Public Interest Journalism funded through NZ On Air
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