Stocks of the most common house insulation product, Pink Batts, have been exhausted outside of Auckland.
The pandemic's severing of the supply chain from Auckland is threatening shortages of common building materials.
Fletcher Building says it has stopped making Batts under alert level 4, and even in Auckland has only "extremely limited" stock.
"We can confirm stock levels have been fully exhausted outside of Auckland," a spokesperson said.
"We have been following the level 4 lockdown rules which requires us to halt manufacturing - this means we also only have extremely limited stock remaining in our Auckland manufacturing and distribution facility."
It would take just 24 hours to get production running again, as the Auckland site "can operate with a skeleton team adhering to public health rules".
It was not correct that once production restarted, supplying the Auckland market would have priority over other places, the company said.
Several construction suppliers have asked permission to restart operations, however, the Health Ministry has not granted any manufacturing exemptions under level 4.