Labour wants the Commerce Commission to be given more powers to fight what the Opposition says is anti-competitive behaviour in the building industry.
It follows last night's story by 3D Investigates, which uncovered a number of practices keeping New Zealand building materials high.
They include rebates and loyalty offers such as overseas trips, which are designed to keep builders loyal to a particular type of product.
Labour's housing spokesman, Phil Twyford, says companies need to be upfront if they have deals with a supplier.
"Transparency for the retailers could be a good thing. If you walk into Bunnings or ITM, they should have a sign up; they should tell their customers, 'We've got a deal with brand whatever for plasterboard, and that's the only thing we're offering.'"
Building materials in New Zealand are about 30 percent more expensive than in Australia and 60 percent more than in the United States.