Government ministers have agreed in principle to introduce plain packaging laws by the end of this year, as part of a bid to make the country smoke free by 2025.
A similar law in Australia has drawn a lawsuit from tobacco companies who say it violates intellectual properties.
But Professor Jane Kelsey says the Trans Pacific Partnership trade agreement now being negotiated could undermine New Zealand's ability to fight lawsuits from the tobacco industry.
Two big tobacco companies already say they will fight government plans for plain packaging.
British American Tobacco and Imperial Tobacco - which are already suing the Australian government - have threatened to take similar action if plain packaging is introduced in New Zealand.
On Thursday the Government announced that it had agreed in principle to introduce the packaging, to bring New Zealand into line with Australia.
British American Tobacco says it's a step too far and it will take every action necessary to protect its right to display its brand.
Another company, Philip Morris, says plain packaging violates numerous international laws and trade treaties and will not reduce smoking rates.
The Government says it will consult the public later this year before making a final decision.
They won't win - Turia
Associate Health Minister Tariana Turia says that even if tobacco companies take action against the plan, they will not win.
[image:5027:third:right]Mrs Turia told Morning Report that New Zealand has rules in place that provide protection to such legislation that Australia doesn't.
She says she feels very sure that the companies would not win if they took on the Government. She adds that she doesn't want to spend taxpayers' money on court action but would do it to save New Zealanders' lives.
Green Party co-leader Metiria Turei is warning, however, that the Trans Pacific Partnership (TPP) trade deal currently being negotiated could der ail plans to introduce plain packaging.
Mrs Turia says New Zealand has free-trade agreements that provide protection against the kind of litigation expected from tobacco companies, but Ms Turei says the TPP - due to be signed later this year - could allow them to claim that the policy affects their commercial interests.
She says the Government needs to ensure the TPP is not signed until the tobacco packaging decision is made.
Governments 'should not be intimidated'
The chief executive of the Australian arm of the anti-smoking lobby, ASH, says governments should not be intimidated by tobacco companies resisting attempts to introduce plain packaging.
A High Court case brought by tobacco companies is under way in Australia, where legislation on plain packaging will take effect in September.
ASH Australia's Anne Jones told Nine to Noon it's clear why the companies are fighting so hard against the legislation: "I think they know that this is going to work, it is going to reduce the number of people who become addicted to their products, and that's going to affect their profits."
Jonathan Aumonier-Ward, a senior associate with the intellectual property firm A J Park, told the programme other countries are closely watching Australia as it takes the lead on this issue.
He says the legal action in Australia is likely to set a precedent that will make it easier for the New Zealand government to introduce plain packaging.
