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It would cover assets such as land, shares, investment properties, business assets and intellectual property.
The family home, however, would be exempt, as would cars, boats and art.
A capital gains tax (CGT) would apply from April 2021 and would mean a person who sells a second property after that date and makes a $50,000 profit would face a $16,600 tax bill.
That would worry the thousands of New Zealanders who own a second property.
The criticism has been extensive, National calling it an "attack on the Kiwi way of life" and business groups saying the CGT costs would outweigh its benefits.
But Finance Minister Grant Robertson said any recommendations the Government did adopt from the Tax Working Group, headed by Sir Michael Cullen, would be done so as to support fairness in the tax system.
A CGT would probably have a disproportionate effect on older New Zealanders and baby-boomers, who own the vast majority of the assets that would be taxed under the working group's proposal.
With the $8billion raised from the CGT, the Government would have a number of other options for taxation - one being a tax cut for low and middle-income earners.
The group recommended increasing the bottom taxation threshold from $14,000 a year to between $20,000 and $22,500.
This would amount to an extra $15-$16 a week in people's pockets, "which doesn't sound like much, but it's significant for people with a low income", Sir Michael said.
The report also said the Government could introduce a water tax and a tax on polluters.
Sir Michael also suggested the way KiwiSaver was taxed could be looked at. The working group suggests the scheme be tweaked to increase the incentives for low-income earners to save.
It recommended an exemption on the employer contributions for those who earn under $48,000 with a graduated refund for those who earn between $48,000 and $70,000.
Any CGT would take effect only in April 2021.
Any capital gains would be added to the seller's overall yearly income and would be set at the income-earner's top tax rate, likely to be 33% for most The Government will release its official response to the recommendations in April.
But National Leader Simon Bridges was wasting no time, saying soon after the report came out that its recommendations were an "attack on the Kiwi way of life".
"This would hit every New Zealander with a KiwiSaver, shares, investment property, a small business, a lifestyle block, a bach or even an empty section."
Act New Zealand leader David Seymour said the recommendations were "offensive to New Zealand values".
The response from the other side of the political aisle was far more restrained.
Prime Minister Jacinda Ardern said the Government would take the time to assess the report and its proposals.
"We build consensus, and that's exactly the process we will adopt in this case."
Greens co-leader James Shaw was singing a similar tune, as was New Zealand First Leader Winston Peters, for the most part.