A prominent critic of the CPTPP deal says deals the Government struck with other signatories have done little to stop the country being sued.
The Comprehensive and Progressive Trans-Pacific Partnership agreement was signed in Chile earlier this week, bringing an end to a decade of stop-start negotiations, punctuated by protests.
Five countries signed deals with New Zealand promising not to sue - Australia, Brunei Darussalam, Malaysia, Peru and Vietnam. Canada and Chile didn't make any promises, except to use the investor-state dispute settlement (ISDS) clauses "responsibly".
But University of Auckland professor Jane Kelsey said the side letters - as they're called - are just a "desperate attempt to put a gloss on a profoundly unprogressive deal".
She said Australia already had a deal with New Zealand, and of the other four nations, only Malaysia has significant investments here.
"Yet its side-letter does not block Malaysia's investors from using ISDS. New Zealand would have to positively veto a dispute."
The CPTPP may even make it easier for Singaporean companies to launch legal action, said Prof Kelsey.
"The free trade agreement in 2001 required the Government's consent before a Singaporean investor could bring an ISDS dispute. A new side-letter says Singapore's investors can use the right under [CPTPP] to sue New Zealand, presumably without its consent.
"This outcome does nothing to assuage our fears that the Government will capitulate again on its promises to abandon ISDS and to adopt a new inclusive and progressive approach to international trade relationships and agreements."
Trade Minister David Parker said there was very little risk of being sued.
"We haven't been able to get every country on board, but signing letters with this many CPTPP partners is a real achievement," he said on Friday.
Prof Kelsey also took issue with the timing of the signing - which took place on International Women's Day.
"They promise to make the [CPTPP] work for women, indigenous peoples, small and medium enterprises, workers, the environment. Yet those constituencies have repeatedly made it clear that the deal itself is anathema to their interests."
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The CPTPP is expected to be approved by Parliament, with support from National. Labour's allies the Greens are opposed to the deal.
Labour opposed the deal whilst in Opposition, but changed its mind after securing "four-and-a-half" of its five non-negotiables, Mr Parker said.