Companies that fit tow bars are calling on the Transport Agency to cough up for those which need to be recertified.

The NZTA says tow bars which were given the stamp of approval by their appointed certifier, Patrick Chu, have to be re-done at the owners' expense.

But truck owners don't want to pay for re-certification again, so they're asking the company who fit the tow bar to meet the cost, which can be up to a $1,000.

One company that is affected is Just Trucks in South Auckland.

Managing director Mike Childs told Larry Williams he's at his wit's end.

"I do think that there is a bit of a can of worms here that needs to be resolved as I think we are being unduly punished."

Childs says that customers were initially told they could just take the trucks to have the tow bars checked, but then they were told the next day they couldn't use their tow bars.

He says they have been given until November to fix the problem, but that customers want him and his company to sort it out.

New engineers have checked tow bars for his company and have not found issues, but they still have to pay for a new re-certification.

Childs says there was a similar case in the South Island, and the NZTA paid for that to be rectified.

"We think a precedent has been set by the fact they paid out as it was supposed to cause an economic downturn in the region if it wasn't resolved quickly.

"Why they can't do it in this situation, I can't find a reason."

In a statement, NZTA said that in the Chu case, all certifications were able to be revoked and the vehicles were unable to be used for towing until they were recertified.

Chu has since had his license revoked, though Childs says that NZTA has not revealed why he was struck off.