Motorists may be asked to pay twice if their car fails a warrant of fitness check.
New Land Transport Safety Authority rules, to take effect on March 1, give garages and testing stations the right to charge a re-check fee for vehicles which flunk the warrant check.
Until now motoristswhose cars failed the test have had 28 days to make repairs and return for a free re-check.
But the LTSA believes mechanics should be paid for the time they spend re-checking vehicles and it hopes the new regime will also reinforce car owners' legal responsibility to maintain their vehicles in a safe condition.
The vice president of the Motor Trade Association, David Ballantyne, said drivers whose cars failed a warrant test on one or two minor points were unlikely to face a second bill for a check-over once repairs had been done.
Motor industry competition meant a second charge would probably only be asked for if a vehicle failed the test on a number of points and a substantial re-examination was required, he said.
Mr Dobson said a small number of drivers "use the warrant of fitness check as a grocery list" and then make minimal repairs during the 28-day grace period.
The Land Transport Safety Authority's safer vehicles policy manager, Simon Whiteley, said the new rule would end the subsidy drivers of safe vehicles have been paying for those type of car owners.
"There is a tendency for people to wait until the test to find out what is wrong and then get it fixed. Since there is no charge for re-taking the test there is no incentive for people to keep their vehicles in good condition between the WoFs. Effectively those who present their vehicles in good condition and pass are cross-subsidising those who don't."
Meanwhile an LTSA proposal to reduce warrant checks to once a year has been condemned by the MTA.
Currently all vehicles over six-years-old must be checked every six months.
The association's president, Trish Campbell, said any move to annual checks needed to be properly researched and have proven safety benefits.
While annual check-ups were common overseas, several countries were considering switching to a more stringent system like New Zealand's, she said.
