San Francisco startup Comma.ai on Friday said it is abandoning a high-profile effort to develop an aftermarket device to enable vehicles to drive themselves, after U.S. regulators said they could prohibit sale of the product.

The intervention, by the U.S. National Highway Traffic Safety Administration, came before Comma.ai began marketing its device. It is the latest signal that regulators want more control over the development and deployment of self-driving vehicle systems by vehicle manufacturers and suppliers, after a period in which they took a largely hands-off approach.

The NHTSA on Friday disclosed an Oct. 27 letter to Comma.ai stating that the agency is investigating whether the company’s device, called Comma One, complies with federal regulations. The letter and an accompanying special order demanded that Comma.ai provide the agency with information about the device and warned that the agency could prohibit the sale of the system if it were found to be defective.

Comma.ai said on Twitter it is abandoning the device and redirecting its efforts to other products.

The more assertive approach from regulators follows the death in May of the driver of a Tesla Motors Inc Model S sedan that was operating on what the Silicon Valley electric automaker calls “Autopilot” mode.

NHTSA recently released guidelines for self-driving vehicles and systems, indicating its intent to provide more oversight before such systems reach the market.

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The California Department of Motor Vehicles in January sent Comma.ai founder George Hotz a cease-and-desist letter. Hotz responded that Comma One did not fall under the state’s requirements because it is not a fully self-driving system and instead requires constant monitoring and intervention by the driver.

The NHTSA letter was also addressed to Hotz.