Uber's self-driving car service might be driven off-track, after the California highways regulator ordered it to pull the service hours after it was launched.
Uber had started giving passengers the option of a self-driving car with a safety driver when booking a journey. Regulators said the ride-hailing app firm had to stop immediately and get a permit, or risk legal action.
The firm had only just began a public trial in San Francisco, but Brian Soublet, chief counsel at California's Department of Motor Vehicles, wrote a letter to Uber saying the pilot was "illegal" without the same testing permit for autonomous vehicles that other rivals, including General Motors and Tesla, have obtained.
"Any action by Uber to continue the operation of vehicles equipped with autonomous technology on public streets must cease until Uber complies," he wrote. "If Uber does not confirm immediately that it will stop its launch and seek a testing permit, DMV will initiate legal action, including, but not limited to, seeking injunctive relief."
Uber though, has said its cars don't need a permit. In a blog post on the company website by Anthony Levandowski, head of the advanced technology group, it says:
We understand that there is a debate over whether or not we need a testing permit to launch self-driving Ubers in San Francisco. We have looked at this issue carefully and we don’t believe we do.
The reason being, Uber thinks the rules apply to cars "that can drive without someone controlling or monitoring them", and its vehicles are at an earlier stage and aren't ready to drive without someone monitoring them.
The vehicles have tech allowing them to navigate on their own, although drivers sit behind the wheel and can take control when needed.
Levandowski also contrasted California's rules with Pittsburgh, Arizona, Nevada and Florida, saying that "complex rules and requirements could have the unintended consequence of slowing innovation".
It comes after a video of an Uber self-driving vehicle running a red light in San Francisco was uploaded to YouTube. Uber said this was due to "human error". The firm told Bloomberg the car was being driven by a person at the time of the incident. "This is why we believe so much in making the roads safer by building self-driving Ubers."
Uber has been approached for comment.