The fast-tracking of new fire safety rules, prompted in part by the Grenfell Tower disaster in the UK, is expected to add costs and delays to major building projects.
The Ministry of Business, Innovation and Employment in a consultation document in May promised a five-month transition period. Instead some people were told last week.
That prompted one of Australasia's leading fire engineers, New Zealander Tony Enright of Melbourne to write in an online commentary: "MBIE. You are clowns. Unfortunately, you are not funny. This is going to cause a shock in the industry."
The change, which takes effect on Friday, covers hospitals, care homes, high-rises of over 20 storeys, stadiums, big transport terminals, buildings storing dangerous goods and large shopping malls.
Dr Enright said the ministry had proposed dozens of changes to add to the rules around these buildings.
But it then then did a U-turn, and shifted the buildings from one set of fire design rules into another, where there are more checks made by local councils and Fire and Emergency New Zealand, previously called the Fire Service.
"You are doing none of what you said you would do, instead you are doing something you said you would not do," Dr Enright said.
Engineers and architects agree that buildings currently planned but not consented face extra costs and delays while their fire designs are gone over again.
"Had a few difficult conversations last night to clients about malls," one engineer posted to an online forum.
Michael James, of the Society of Fire Protection Engineers, said projects can take up to one or two years to design so there was "quite a bit of uncertainty to building owners and designers to have to go back and complete that loop again".
Architects Institute's chief executive Teena Hale-Pennington said the institute's members would be concerned about costs, the further information required and getting relevant expertise to compile documents for consent.
Ms Hale-Pennington said she learned last Wednesday the fire rules change was imminent and has sent 70 pages of information from the ministry to her members to go through before Friday.
"We would have hoped that there might have been some earlier communication."
The change comes when the construction industry is especially busy in the year-end rush to get projects over the starting line.
A building industry group says there needs to be agreement on how fire safety provisions for new large buildings can be verified.
Amended fire rules - triggered in part by the Grenfell Tower disaster in England - kick in this week covering high-rises over 20- storeys, hospitals, care homes and large shopping malls.
But fire engineers and architects are calling on the Ministry of Business, Innovation and Employment to delay the change, due to start on Friday.
Building Industry Federation chief executive, Bruce Kohn said the short time between the ministry's decision and its implementation will lead to big costs for firms which are in the process of designing such buildings.
"The problem is that it's left to the judgement of individuals, whereas if we have agreement between fire engineers at the councils and MBIE on precisely the safety mechanisms which should be in place, then everyone knows what the plans should look like," Mr Kohn said.
Mr Kohn said an agreement would mean companies did not face different decisions from compliance officers and fire safety engineers.
The Property Council was taking a wait-and-see approach.
The Ministry of Business, Innovation and Employment said it did not have time to prepare a response for RNZ, but provided the letter it sent last week to engineers and architects.
"A transition period ... is not considered necessary as the changes merely clarify its intended and appropriate use [of the fire rules]," it told them.
"We are giving you advance notice so you can prepare for the change with your respective organisations."