The National Highway Traffic Safety Administration on Friday opened an investigation into whether 1,000 Tesla Cybercab vehicles were properly certified.
Tesla shares fell more than 6% on Friday.
The auto safety regulator is examining the process and technical data the EV maker relied on to claim compliance with federal motor vehicle safety standards.
The probe comes after Tesla on Thursday began commercial deployment of a small number of the two-seater Cybercab in Austin, Texas, and said it planned to gradually expand the service to additional vehicles and locations.
NHTSA said the Cybercab lacks permanently attached conventional manual controls, including a steering wheel, brake pedal, accelerator pedal and mirrors.
The agency said it would examine the basis for Tesla’s certification and related issues, including the extent to which the company determined that certain Federal Motor Vehicle Safety Standards were not applicable to the vehicle.
Tesla did not immediately respond to a request for comment.
The EV maker had 420 autonomous vehicles registered in Texas as of Friday morning, according to state records, including 45 Cybercab vehicles.
In June, the agency proposed to end a government requirement for manual brake pedals in self-driving vehicles, a move that would make it easier to deploy such vehicles on US roads. It has proposed other changes to federal safety standards to allow AVs to avoid needing additional human driver equipment.
Under existing law, fully self-driving vehicles do not need NHTSA approval if they have required human controls, like steering wheels, brake pedals or mirrors.
NHTSA has authority to grant petitions to allow up to 2,500 vehicles per manufacturer yearly to operate on US roads without required human controls. In July, NHTSA approved a petition for Amazon’s Zoox unit for limited commercial deployment of its novel steering-wheel-free robotaxis, a first for the autonomous ride industry.