Building and homeowners organisations say the use of substandard products in construction is "very concerning", and may be under-reported.
Auckland Council said as the city's construction boom gained momentum, traditional building materials were becoming harder to find and some builders were turning to alternative products which were not always up to standard.
Homeowners and Buyers Association chief executive Roger Levie said pressure on the industry was resulting in unethical practices.
"From our point of view it's very concerning," Levie said. "If someone's buying a spec house [for example] you really don't have any way of knowing what's gone into that house," he said.
"There's a huge amount of reliance now being put on the council and inspection process and it is really positive to see that council is picking these things up ... but I imagine for everything they are picking up there is a whole lot of stuff that they simply miss because they're so busy."
Ian McCormick, general manager of Auckland Council's building control team said council building inspectors were seeing more substitutions than ever before, with a cheaper price being the number one reason for replacing the specified product.
McCormick urged builders to save themselves and their customers thousands of dollars by getting the proper signoffs before using substitutes.
"We're seeing innovative new products and processes entering the market," McCormick said.
"That's great news because it improves the whole industry. Auckland Council has a duty of care to Aucklanders to make sure those products meet our high standards and are fit for the intended use for the lifetime of the building."
McCormick was aware of a number of incidents where non-compliant products had been used, and had to be removed.
In one case, a home owner was forced to replace a new roof after the company could not prove compliance to the Council.
Another case resulted in electric wiring in four homes being removed after being deemed non-compliant - resulting in thousands of dollars of costs for the developer.
McCormick said he was also aware of issues in the pre-cast concrete panel industry which was struggling to keep up with demand.
"While we recognise builders need to get on with their construction, we can't cut corners on quality, durability and suitability," McCormick said.
"While there are some great new products on the market, the boom has attracted a few cowboys trying to cut corners and some importers trying to bring in cheap, substandard products."
Certified Builders chief executive Grant Florence said he was aware of the issue and was encouraging members to plan ahead and get orders in early to avoid lag-time or product shortages.
"Because we've got this building boom, it's a bit of economics," Florence said.
"Where there's a higher demand for materials, and if the local supply can't meet that in a timely manner, then other people may see an opportunity and step in and provide this type of material," he said.
"But we definitely encourage [the industry] to use materials that are certified or have been appraised here in New Zealand."
Registered Master Builders chief executive David Kelly said there was no question that the amount of work in Auckland, and to a lesser degree Hamilton and the Bay of Plenty, meant extended lead times for supplies.
He highlighted pre-cast panels as particularly bad but said a number of other areas including aluminium joinery and pre-nailed frames for houses were also in high demand.
Kelly said while he hadn't heard of members using substitute products, he was concerned about newcomers to the industry that were not as knowledgeable.
"There is a danger those people will take shortcuts and that is a concern to the industry generally - that people who are new don't really understand what the requirements are and don't do their homework, so they end up substituting a product that they shouldn't," Kelly said.
"With our members ... they have experience in business so generally they know the industry, they've been through the ups and downs and they know what to look out for."
McCormick said while it was great to see innovative new products and competition in the market, cutting corners was only going to result in problems for all involved, and if a deal looked too good to be true, it probably was.