A building watchdog is intervening to make sure problems with key consent documents are handled fairly in Wairarapa.
Masterton District Council has warned 640 building owners who never got a code compliance certificate for work done years ago that they might be refused one now.
One owner complained the council was breaking the law.
International Accreditation New Zealand (IANZ), which accredits building consent authorities, is looking into the complaint.
It had ordered the council to review how it handled issuing code compliance certificates and its communications with property owners, the Ministry of Business, Innovation and Employment said.
Some owners have got belated certificates after talking to the council.
IANZ was scheduled to carry out a regular assessment of the district council last week, so the ministry asked it to consider the complaint, in terms of any accreditation issues, the ministry's building system assurance manager Simon Thomas said in a statement.
The council has stressed that when it told owners that a certificate was being refused "at this time", this left the way open for them to sort it out with the council.
Certificates are meant to be issued within two years of a building consent kicking in, but in some cases in Wairarapa, projects stretching back to 1992 had not got a certificate, which is the responsibility of a building owner to obtain.
"IANZ will require the council to review its documented procedures around the decision to issue or refuse to issue CCCs," Thomas said.
"IANZ will work with the council to ... ensure that the proper systems are in place to enable better decisions and communications to occur in future."
The ministry had contacted the council and would keep a watch out to see if any other action was needed over the complaint, he said.
The District Council said it now had processes in place to remind property owners of the timeframes around certificates, and a system for sending them reminder letters at the 10-month, 21-month and 24-month marks.