The Green Party would nearly double the tax foreign tourists pay at the border to fund conservation efforts and regional tourism.
Its so-called "Taonga Levy" would increase current border charges for international visitors by between $14 to $18 to a total border levy of around $40.
The Greens' proposed tax, not applicable to Kiwis, would be split 70-30 toward the just-announced Predator Free New Zealand (PFNZ) effort and the Regional Mid-sized Tourism Facilities Fund.
Outlining the policy at the Environmental Defence Society's annual conference in Auckland today, party leader James Shaw said the new tax would generate about $46 million each year for PFNZ, or $1.5 billion by its zero-pest predator goal of 2050.
It would also raise about $80 million over four years for the regional tourism fund.
Shaw argued that both areas were under-funded by the Government, which has committed $28 million toward the public-private PFNZ effort, and $12 million over four years to the regional tourism in this year's Budget.
"The Taonga Levy will bring in tens of millions of dollars every year to help make New Zealand's dream of being predator-free a reality, and help tourism hotspots cope with rising visitor numbers."
With annual visitor numbers expected to reach 4.5 million by 2022, the raised tax would allow tourism destinations to deal with strains on infrastructure while protecting the environment, Shaw said.
"Small communities on the West Coast and Coromandel shouldn't be expected to wear massive rate hikes to upgrade sewerage systems to cope with the influx of tourists.
"National has done the absolute bare minimum to help councils, promising just $3 million a year to help fund new tourism infrastructure. It's a token gesture at best."
The party noted the tax was still lower than the NZ$58 border charge to enter Australia, or the NZ$127 that the UK charged visitors.
"I think most visitors to New Zealand will understand that paying an extra $14 to $18 is worth it to help protect our unique environment and native wildlife."
Aside from people who live in New Zealand, the tax would not apply to some, including children under two years of age, air and cruise crew, and military, diplomatic, or government passengers.
Responding to the announcement, Prime Minister John Key said the private sector was already itself reviewing whether tourist levy of some sort should be applied.
"I'm not discouraging them from looking at the issue," he said.
Key said the levy the Greens were suggesting was for something the Government was already funding.
"If we were to progress a levy of some sort we would really strongly argue it'd be about tourism infrastructure in some form or marketing."
The Government had explored applying a departure tax a number of years ago, he said.
"In the end we decided the economy was weaker in tourism numbers at that point so we decided to put more money into tourism directly out of the budget
"These things aren't straightforward.
"If you get a departure tax there's no real way of stopping New Zealanders who go away from paying that."
The Government is presently waiting for recommendations from a group of private sector players led by Air New Zealand.
Tourism Export Council chief executive Lesley Immink was pleased to see the policy being discussed.
"I think the timing is really good, I don't think the number is going to affect any of our international visitors whatsoever, and if anything, we can leverage off it as a marketing tool.
"However, we do need to be careful that what we are doing is giving any government permission just to keep taxing international visitors as they see fit."
Tourism Industry Aotearoa chief executive Chris Roberts questioned the idea.
"We agree that both Predator Free New Zealand and the tourism infrastructure fund deserve a boost in funding, but really, is a new tax the answer to a funding issue?
"In our view, our international visitors are already heavily taxed, because they are paying over $1 billion a year in GST - so they are already more than paying their way."
Environmental groups have meanwhile welcomed the levy.
"Our nature is our value proposition for international tourists," said Environmental Defence Society policy analyst Dr Marie Brown, author of the book Vanishing Nature: facing New Zealand's biodiversity crisis.
Right now, our biodiversity is struggling due to underfunding and local communities are struggling to provide infrastructure," she said.
"This novel mechanism would provide an additional stream of funding to these key priorities, to complement the work of government, the private sector and NGOs.
"The quantum is a great start, and long term there might be a good case to increase it even further."
Forest and Bird's advocacy and campaigns manager Kevin Hackwell believed an extra $46 million each year would move New Zealand's dream of becoming predator free by 2050 forward "significantly".
"The present Government has already committed $7 million a year to achieving a predator-free New Zealand by 2050 and the $46 million raised from a taonga levy tax would mean a six-fold increase in the funding already promised."
Tourism New Zealand would not comment on the policy.