Tesla (TSLA) Cybercab is under investigation by the US National Highway Traffic Safety Administration over the process used to claim compliance with federal vehicle safety standards, the regulator said Thursday.

Tesla began commercial use of a small number of its Cybercabs in Austin, citing safety data it claimed showed it was compliant with all rules, the regulator said.

But the regulator said the vehicles lack permanently attached conventional manual controls, such as a brake pedal, gas pedal, steering wheel, and mirrors, the regulator said.

The agency said it was launching the investigation into an estimated 1,000 vehicles to examine "the process and technical data on which Tesla relied when certifying the Cybercab."

It will also examine whether Tesla's certification depended on its own decision that certain federal criteria were not applicable to the Cybercab, the regulator said.

Tesla did not immediately reply to MT Newswires' request for comment.

Shares of the company were down more than 2% in recent premarket trading.