Uber is under fire for rolling out self-driving cars in San Francisco without a permit, which state regulators say is illegal.

The California Department of Motor Vehicles has ordered the ride-hailing firm to cease its autonomous vehicles operations, threatening legal action if "Uber does not confirm immediately that it will stop its launch and seek a testing permit."

Uber began deploying driverless cars in San Francisco on Wednesday as part of the company’s expanded public test of autonomous vehicle technology. Semi-driverless cars have been picking up Uber passengers in Pittsburgh for months.

An Uber employee is still behind the wheel of the car to take control if the vehicle falters or can’t handle a portion of a ride.

In a blog post, Uber acknowledged that there was some debate about whether it needs a permit to test driverless cars in California. But the firm concluded it didn't need one because those rules only apply to cars that can drive without someone controlling or monitoring them, and because its operations will be similar to the Pittsburgh pilot program.

“We have looked at this issue carefully and we don’t believe we do,” Uber said.

Though Uber has warmed up to working with regulators over the years, this isn’t the first time the company started operating first and dealt with regulators later. In 2013, Uber’s first cease and desist letter came from a governmental authority just months after the service launched.

“Several cities and states have recognized that complex rules and requirements could have the unintended consequence of slowing innovation,” Uber said Wednesday. “Our hope is that California, our home state and a leader in much of the world’s dynamism, will take a similar view.”

Currently, 20 other companies have permits to test self-driving vehicles in the state. The permits require that companies have insurance coverage of $5 million, file reports of any crashes and submit an annual “disengagement” report.

“Uber is threatening public safety and trying to avoid providing important information about its activities,” said John M. Simpson, privacy project director for Consumer Watchdog. “Using public roads as your laboratory carries responsibilities. Uber is ignoring them and shamefully flouting important safety requirements. It must be stopped immediately.”