The deal is likely to pass through Parliament with plenty of support - National has long supported the deal, and the bulk of negotiations were conducted when National was in power.

One of the questions put to Ms Ardern at Rātana is whether Labour's decision to support the deal is a U-turn.

Thousands marched against the TPP when National was in power. Labour Party politicians were among protesters, and the party said it would not support the deal unless five "non-negotiable bottom lines" were met.

Trade Minister David Parker says those conditions have been met.

Ms Ardern says Labour fought for and got "significant concessions" and it's now a "vastly improved" deal.

"It's not a new position. Since we came into Government we said straight away, 'We are going to change the mandate. We're going to push hard on the issues we said are important to us.' That's exactly what we did."

One of the issues raised by opponents of the TPP is investor state dispute settlement (ISDS) clauses, a mechanism which could be used by investors to sue countries for discriminatory practices. Opponents, including researcher Jane Kelsey, say the courts would impinge on a country's sovereignty.

But Ms Ardern insists the ISDS clauses have been improved, and says when the TPP comes up for review, the Government would "hope to raise issues with the ISDS clauses again."

"There are significant changes. Before we went into this, the ISDS clauses were much more broadly applied.

"We now have a suspension of those clauses for investor screening. We've made the kind of changes that mean this agreement is much more aligned with other FTAs we've signed up to."

The Green Party, though, says the changes don't go far enough.

"We recognise Trade Minister David Parker has made significant progress on some controversial provisions in the TPP, including investor-state dispute settlement, and we support those changes. However, we still don't believe there are sufficient safeguards for people and the environment that would enable us to support the deal," co-leader James Shaw said.