UPDATED 3.05PM: A legal challenge will be lodged in the High Court next week contesting secrecy around the Trans-Pacific Partnership free trade negotiations.

Outspoken TPPA critic Professor Jane Kelsey was met with a blanket refusal when she made an Official Information Request to Trade Minister Tim Groser back in January.

She made the request on the back of a decision from the EU Ombudsman that the consequences of a deal being discussed between the EU and the US, TTIP, were so great that the people of Europe needed to see much more detail, and produced a long list of what needed to be produced.

When her OIA request was denied, the Minister's refusal had to be reviewed by the Ombudsman before any court action could be lodged. Professor Kelsey only received that Ombudsman's report on Wednesday - four and a half months later.

She and a number of groups, including Consumer NZ, the Association of Salaried Medical Specialists, Greenpeace and Oxfam, are now heading to the High Court, with an urgent application for a judicial review.

"The secrecy surrounding the negotiations is, in my view unprecedented," Professor Kelsey said. "Especially given the parties signed a pact right at the beginning that they wouldn't release any documents during the negotiations, and they keep all but the text secret for another four years beyond that. The stakes are too high here to allow that to go unchallenged."

Professor Kelsey said while they would have preferred to have brought the case earlier, it remains crucially important to secure release of information before any deal is done and dusted, and to clarify the rules for future negotiations.

She said the case will go ahead no matter what happens in Hawaii this weekend, where negotiations on the 12-country Pacific trade pact could wrap up.

"It's very disappointing it took the Ombudsman's office so long, because ideally we would have liked to have had it before the Ministerial meeting that will supposedly bring [the TPPA] to an end.

"But there are many other processes where getting that information is important. Not only the debate that happens about the conclusion of the agreement, but there is also a process that the US will adopt called certification, which is where the US puts a lot of pressure on our Government to change what we've done domestically to comply with the agreement. And that needs to be out in the open. And in the current disposition of the Minister, that would take place in secrecy."

Professor Kelsey said the challenge is important not just for the TPPA, but any future agreements were negotiations are veiled.