Oxfam says it is "shocked" by new research showing New Zealand's two wealthiest men own as much as the poorest 30 percent of Kiwis combined.
The organisation's report, An Economy for the 99 Percent, was released on Monday at 1pm.
It shows the richest 1 percent of Kiwis possess 20 percent of the country's wealth, while the vast majority - 90 percent - own less than half.
"The gap between the extremely wealthy and the rest of us is greater than we thought, and it's trapping huge numbers of people in poverty and really fracturing our society," says Oxfam executive director Rachel Le Mesurier.
New Zealand's two richest men - Graeme Hart and Richard Chandler - have an estimated $12.8 billion between them, according to the report. Mr Chandler's name popped up in the Panama Papers last year - with his Singapore-based Richard Chandler Corporation using Mossack Fonseca to set up two companies in tax haven the Bahamas.
Ms Le Mesurier says Kiwis love fairness, not inequality, and the Government needs to crack down on tax avoidance to curb it.
"There are significant drivers of this inequality. One of those is that for the extremely wealthy, there is a focus on delivering to shareholders, in many cases at all costs. That can mean avoiding tax or finding loopholes that are legal on the face of it, but not fair.
"That impacts on small businesses who are paying their tax fairly and have to pick up the burden of that."
Figures from Inland Revenue cited in the report show that of the 252 Kiwis worth more than $50 million, a third declared an income of less than $70,000 - where the top income tax rate of 33 percent kicks in.
Oxfam also says big businesses and the "extremely wealthy" are avoiding taxes, keeping wages down and paying producers less.
Critics of the report, such as the pro-business think tank the NZ Initiative, say it's flawed because it compares absolute wealth, not earning potential or incomes.
For example, a recently graduated doctor would have a large student debt, making them poorer than most Kiwis in the eyes of this report.
Statistics NZ in July last year said the richest 10 percent of Kiwis owned 60 percent of the country's wealth, and the richest 1 percent held 18 percent - slightly less than what Oxfam's report claims.
"The IMF themselves have said that this type of gap, and inequality increasing as it is, has a real risk of causing disenfranchised populations - and we've seen that with both Brexit and the Trump election," says Ms Le Mesurier.
Then-Prime Minister John Key said the figures had become worse because "better-off New Zealanders will own assets, particularly houses, and those house prices have been rising".
Previous Statistics NZ reports show between 2003 and 2010, the top 10 percent of Kiwis had around 55 percent of the wealth. This expanded to 60 percent by 2016.
Today's report is released to coincide with the annual meeting of political and business leaders at the World Economic Forum in Davos, Switzerland. Trade Minister Todd McClay is expected to attend.