New Zealand is losing more than $700 million a year as a result of profit shifting schemes by multinational companies, a new study has found.
The figure is more than double the $300m estimate given this month by ministers Judith Collins and Steven Joyce, when they announced proposals to crack down on tax-avoiding multinationals.
The study, carried out by the UK-based Tax Justice Network using 2013 data, found global losses as a result of profit shifting amounted to about US$500 billion ($711b) a year.
The organisation describes profit shifting as the process of companies moving profits from their subsidiaries in higher-tax countries - where the real economic activity takes place - to other subsidiaries in tax havens.
This is typically achieved by the company setting up internal trades which exploit international tax rules to move taxable profits from one jurisdiction to another.
In response to questions, a statement from Revenue Minister Collins said the $300m figure was based on information Inland Revenue had compiled through tax returns, investigations and surveys of companies operating in New Zealand. She said it was more detailed and specific to New Zealand than the Tax Justice Network's $700m estimate.
"The OECD maintains that estimating the revenue impact of BEPS [base erosion and profit shifting] is difficult from a global perspective," said Collins. "The best source of information concerning the loss of revenue to BEPS in any country is the revenue authority in the jurisdiction itself."
She said the three BEPS consultation papers released by the Government this month were an important part of the solution, as was New Zealand's adoption of the Multilateral Convention to Implement Tax Treaty Related Measures to Prevent BEPS.
University of Auckland tax expert Michael Littlewood, a professor of law, said nobody really knew how much New Zealand was missing out on, and that was a big part of the problem.
"Both those figures I think are entirely plausible," he said, adding that the real tally could well be more than $700m.
He said the effectiveness of the Government's proposed new measures remained to be seen.
"Consultation can be a good thing or it can be a bad thing because it can be something that leads to action but it can also be a stalling technique that doesn't achieve much."
Labour Party revenue spokesman Michael Wood said the Government had a history of underestimating the extent of the problem.
"Certainly, other tax experts in New Zealand have estimated it could be between $500m and even $1 billion a year," he said. "So this is pretty much in the range and it confirms it is a serious problem that we have to act on."
Labour was calling for a full inquiry and action on the issue. In addition to the Government's current review, Wood said consideration should be given to introducing a diverted profit tax - or "Google tax" - something the Government had refused to do.
Green Party co-leader James Shaw said the discrepancy between the Government's figures and the Tax Justice Network's estimate highlighted the need for better information.
"I know that it is a very nebulous area but I think the scale of the range shows that the Government needs to put more focus on doing the numbers and on resourcing Inland Revenue to build a clearer picture," he said.
"This sort of thing is fundamentally unfair because it's revenue that the Government could use to invest in infrastructure and public services."
The study was based on data from the International Centre for Tax and Development, using International Monetary Fund methodologies.
It found that lower-income nations were the biggest victims of profit shifting, and in some countries, including Zambia and Argentina, losses exceeded 4 per cent of GDP.