The public has been put in harm's way because the New Zealand Transport Agency has failed to properly monitor safety checks.
An urgent investigation is underway into 150 cases. But it's not clear how many dangerous vehicles could be on the road, among them, heavy vehicles.
Heavy vehicles around the country have safety checks, but the NZTA hasn't properly policed those that do the checking.
And it's now likely there are unsafe vehicles on the road as a result.
"I have expressed my extreme disappointment that the agency has not carried out its regulatory role to the standards that I expect," Transport Minister Phil Twyford said.
NZTA chairman Michael Stiassny said the agency, "cannot say that anyone is proud of where the agency has been or where the safety is".
In some cases the agency let certifying companies police themselves, in others it simply ignored files.
Now 850 compliance files are being reviewed by a law firm, and 152 of those will be urgently reviewed because there's a threat to public safety.
"Sadly this has been going on for a considerable period of time," Mr Stiassny said.
Road Transport Forum chief executive Ken Shirley said the forum has "been very critical of NZTA and not functioning as a regulator in the vehicle compliance, but particularly the heavy vehicle fleet".
NZTA says at this stage there's no evidence to suggest incompetence has resulted in accidents that have caused serious injury. But it will have more of an idea in November when the results of the 152 urgent cases are reported back.
The Transport Minister is blaming under-resourcing by the previous government.
"The loss of personnel in 2014 for heavy vehicle certification inspections I think is an example of that," Mr Twyford said.
National's Transport spokesperson Paul Goldsmith said, "Actually what this is about is him talking about underfunding in order to justify his road taxes that he keeps on piling on".
The law firm carrying out the investigation will continue keeping a close eye on the Transport Agency, with a lawyer now based at its headquarters.