Two major construction companies are looking into their use of steel mesh following an announcement that a supplier has been incorrectly certifying one of its products.
Steel and Tube could face a $600,000 fine from the Commerce Commission for what it says was a genuine mistake.
Steel mesh is used to reinforce buildings but one of the country's largest suppliers is being questioned over their product's integrity.
Steel and Tube have apologised for using the logo of an independent testing laboratory on the certification of its steel mesh, despite the fact the mesh is tested in-house, and not at the lab.
"We left it on inadvertently, and perhaps we should have taken it off," Steel and Tube's Dave Taylor said.
Chris Woudenberg has a testing lab in Auckland that's accredited by an independent auditing body.
Steel and Tube are not accredited and Mr Woudenberg says that's not good enough.
"It's a traceability chain -- it means the person doing the test is competent, the equipment is traceable and accurate, and the test is done professionally," he said.
"A lot of manufacturing organisations do in-house testing. We make sure that various key parts of the equipment are calibrated from time to time, so we follow the regime rigorously."
According to Mr Taylor hundreds of thousands of the mesh sheets -- predominantly for residential use -- would have been produced with the incorrect logo in the past four years.
Leigh's Construction and Fulton Hogan have told Newshub they're looking into whether they've used any of the Steel and Tube mesh in any of their projects.
The Commerce Commission is investigating the case too.
It says the fact Steel and Tube tests in house is not cause for concern, but mis-using the logo could see them face hundreds of thousands of dollars in fines for breaching the Fair Trading Act.