A law allowing iwi to stop and checks cars is being scrutinised by the Act Party

The change to the Covid-19 Health Response Act grants iwi organisations power to close roads and public places to stop vehicles.

Police have announced they'll work with iwi to check people travelling into Northland after Auckland's border opens on December 15.

But Act leader David Seymour says he wonders if iwi threatened to do it anyway.

He says this whole process may have been reverse engineered to save face, and if so, it's a transfer of sovereignty.