National is vowing to overturn the Government’s support of the United Nations Compact for Migration.

Foreign Affairs and Trade spokesperson Todd McClay says Foreign Minister Winston Peters has sprung the signing on New Zealanders on the last day of Parliament.

Peters says legal advice is the Compact doesn't affect New Zealand's right to make its own migration laws.

But McClay says this is spin, and the document seeks to restrict individual countries' right to set their own immigration policy.

He's asking why, if the Government was unconcerned, has it been so secretive and waited until the very last day of Parliament to front up?

His party leader, Simon Bridges, told Larry Williams he's suspicious about the timing.

"Winston Peters has put out his press release literally after the last day's question time and media scrum, there's no more for this year. [It's an] incredibly cynical, zero accountability move."

He says that he understands that Cabinet was highly divided over the decision.

Bridges says that National is the party most in favour of migration, but that he does not believe this compact is in our interest.

“Just because it’s non-binding, it doesn’t mean it’s of no effect.”

Bridges says the compact treats legal and illegal migration in the same way.

"There is no automatic right to migrate to another country without that country's full agreement, a view which the UN's Global Compact on Migration seeks to counter.

"While not binding, the compact could restrict the ability of future governments to set immigration and foreign policy, and to decide on which migrants are welcome and which aren't."

Bridges says that he feels migration should be something that nations decided on in their own interests.

Speaking on behalf of Peters during Question Time yesterday, Minister David Parker said it was "irresponsible and incorrect" to say that the compact curbs a country's sovereignty.

"The National Party is very lonely in their populist gymnastic," he said, referring to the few countries - including the US and Australia - that have signalled they would vote against it.

Parker further noted that the National-led government had in 2016 voted in favour of a precursor to the compact called the New York Declaration for Refugees and Migrants.

"The reversal by the National Party on its earlier position is desperate, opportunist flip-flop."

LISTEN TO SIMON BRIDGES TALK WITH LARRY WILLIAMS ABOVE