When questioned this week, the agency would not expand on what advice was given, citing legal privilege, but Fortune Manning transport law expert Shafraz Khan said there was no way Uber allowing its drivers to operate without the endorsements was lawful.
"I see no reason why NZTA could not prosecute Uber as a second party to a driver infringement, as they are facilitating the drivers' work without the proper licences," Khan said.
Though Uber drivers were self-employed contractors, it did not absolve the company of responsibility, he said.
Uber did not respond to questions about whether they too had sought legal advice on the matter.
In a report to associate minister of transport Craig Foss on May 9, NZTA access and use manager Celia Patrick said the agency was investigating "potential breaches of the law with a primary focus on [Uber] drivers with a criminal or medical history of concern and complaints received."
"A number of these investigations have already resulted in compliance action including formal warnings and breach notices," Patrick said.
The agency was also taking "enforcement action" against Uber drivers without P endorsements, and investigating any complaints received.
On May 16, Patrick told the minister "we also expect to receive final legal advice on our ability to include Uber as a second party for aiding and abetting offending in the event of prosecution taken against Uber drivers."
Between March 31 and September 23, NZTA sent out 2703 warning letters to prospective Uber drivers, issued 118 formal warnings, 141 infringement notices and ordered 29 drivers off the road.
According to the document, police have undertaken an "Uber operation" at Auckland airport and NZTA was targeting "suspected Uber drivers with high-risk factors such as failed medical or fit and proper checks or suspended or revoked P endorsements."
An Uber spokesman told the Herald that the screening process for its drivers included a criminal background and driving history check.
And unlike NZTA, Uber did not allow anyone with a history of driving under the influence, dangerous or careless driving on the platform - though their conviction checks do not extend outside of New Zealand, and the Clean Slate scheme can clear some convictions older than seven years.
"The Transport Minister has clearly stated that a screening process isn't a panacea for safety - technology and apps now help ensure safety before, during and after a ride in ways that have never been possible before," the spokesman said.
Under the P endorsement system, a driver with a historical conviction - which could include a careless driving conviction, even one that causes injury or death - could still obtain an endorsement, if they had gone on to demonstrate many years of driving without offending, an NZTA spokesman said.
