More than 5000 vehicle owners are being contacted over being issued possible botched warrants of fitness - but more are likely to be added to that list.
Susantha Ranatunga from Onehunga's Church Street Motors and Tyres is the latest inspector to be suspended. Auckland's Jet Tyres and Wheel Alignment has also been stood down as an inspecting organisation, along with worker Anderson Lee.
It brings the total number of Kiwis needing to recheck their vehicles to about 14,000.
Autotalk managing editor Richard Edwards says the current investigation is lengthy, and the New Zealand Transport Agency's (NZTA) failure to regulate vehicle inspectors is hugely costing the taxpayer.
"I think we're up to 14,000 vehicles that haven't had warrant re-checks, at a cost to the Government. You've also got this law firm - they've been on the books for over a month, spending taxpayers' funds to do this work."
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And Mr Edwards says there will be more faulty cases to come.
"Every time you find an issue with one workshop, that could have been two, three, four or five years they've been having those issues. Those places will do dozens of cars a day, for a long period of time."
A legal firm is currently looking into 850 compliance files.
Mr Edwards says NZTA needs to make sure inspectors follow the rules.
"NZTA has perhaps had warnings on companies, or information on companies that hasn't been processed, hasn't been connected A to B, and the appropriate action taken."
NZTA admitted it knew about issues at another dodgy inspector, Dargaville Diesel Specialists, as far back as 2011.
"Given the lack of resources, unfortunately they've not been able to get in and see as many of the inspectors as we would like them to be seeing," said Craig Pomare from the Motor Trade Association.