Less than one day after introducing its self-driving vehicles to the company's San Francisco hometown, Uber has been ordered by the California DMV to stop operating the fleet. If it doesn't comply, the ride-hailing firm will face legal consequences.

Uber's San Francisco pilot program is an expansion of its self-driving car project that launched in Pittsburgh during September. A "handful" of autonomous Volvo XC90 SUVs hit the city's streets on Wednesday morning, but the state's department of motor vehicles wasn't happy about Uber trying to circumvent California's self-driving rules.

It seems that Uber, unlike the twenty other companies that are doing the same thing, never registered for a DMV permit to test its autonomous technology on the state's roads. This wasn't an oversight on Uber's part; the firm says it purposely didn't pursue the permit because its cars have a person behind the wheel at all times monitoring the system, therefore they can't be considered fully autonomous.

The DMV, of course, disagrees. In a letter to Uber, the agency's deputy director and chief counsel, Brian Soublet, wrote: "If Uber does not confirm immediately that it will stop its launch and seek a testing permit, DMV will initiate legal action." The DMV added that the technology "must be tested responsibly."

Interestingly, the letter arrived just after a dash cam video surfaced purportedly showing a driverless Uber running a red light in San Francisco. Luxor cab driver Jessica Felix caught the incident on video (below). She said the front and passenger side seats were occupied, but she couldn't see if anyone was in the back.

After investigating the matter, Uber blamed "human error" and said the car wasn't part of the driverless program. In an emailed statement to Mashable, it said: "This is why we believe so much in making the roads safer by building self-driving Ubers. This vehicle was not part of the pilot and was not carrying customers. The driver involved has been suspended while we continue to investigate."