The building regulator has asked the Commerce Commission to investigate seismic steel reinforcing bar sold by a major supplier.
The Ministry of Business, Innovation and Employment (MBIE) said it had asked the watchdog to investigate "possible misrepresentation" by the supplier, Euro Corporation, after receiving a report on the issue.
Earlier this year, Euro admitted selling rebar marked as 500E, when tests showed it was only 300E.
At the time, Euro said that a manufacturing error had affected a tiny quantity of rebar, an explanation that was accepted by the ministry.
Rebar is one of the most common structural products used to strengthen concrete in a huge range of structures.
But a report from a consulting engineering firm has subsequently raised the issue of whether some of the rebar lacks the unique producer markings that standards require.
The ministry said that after it got that report, it referred the case to the Commerce Commission.
Euro Corporation said its unique markings were part of the deformations on the outside of the rebar, not alpha-numeric ones.
In a statement this afternoon, the company said it only found out the ministry had contacted the commission following RNZ's enquiries.
"Euro is furious that MBIE chose not to give Euro an opportunity to explain our view that the allegation and report are based on a misunderstanding of the standard."
Wellington builder spotted initial marking problem
The case has arisen after a Wellington builder grew suspicious about how easily rebar that had been sold by Bunnings was bending.
He had it tested, and Euro Corp then did its own testing, and said it had told the Malaysian factory Amsteel to correct the error around mis-stamping the steel.
Euro Corp said in its statement this afternoon that it had physically isolated the rebar incorrectly marked as stronger than it actually was.
"That material is still held in quarantine ... We self-reported the issue to MBIE in January, and have kept them informed of our actions throughout."
It has repeatedly offered to put things right with the affected building owner, but has been unable to reach an agreement with them, it said.
The owner alleged some of the bar was unmarked, and commissioned a report to that effect, but this was wrong as the standards allowed for unique deformation patterns to be used as producer markings, it said.
"We deeply regret that MBIE's behaviour could undermine the confidence of any company to self-report an issue in the future. They may therefore have made New Zealand consumers less safe, not more safe."
"We will now take this matter up with the Commerce Commission."
Two main grades of rebar have been specially developed for earthquakes: 500E, which is stronger and allows for greater performance from concrete; and 300E, which is more ductile and easier to weld.