The National Highway Traffic Safety Administration (NHTSA) announced on Thursday that it has launched a formal inquiry into 416,000 Tesla vehicles after receiving allegations of sudden brake activation linked to the company’s driver assistance system Autopilot.

The preliminary assessment covers Tesla Model 3 and Model Y automobiles in the United States from 2021 to 2022, following 354 complaints over the previous nine months. The vehicles under investigation, according to the NHTSA, include Tesla’s Autopilot advanced driver assistance technology, which allows them to brake and steer automatically inside their lanes.

NHTSA said: “Complainants report that the rapid deceleration can occur without warning, at random, and often repeated in a single drive cycle.”

Owners say they have raised concerns with Tesla, which has dismissed the complaints saying the braking is normal, and some have called it “phantom braking”.

The owner of a 2021 Tesla Model Y told NHTSA in October that while driving on a highway at 80 miles per hour “the car braked hard and decelerated from 80 mph to 69 mph in less than a second. The braking was so violent, my head snapped forward and I almost lost control of the car.”

The National Highway Traffic Safety Administration (NHTSA) is increasingly scrutinising Tesla, which is examining many issues. Since October, the electric vehicle manufacturer has issued ten recalls, several of which were prompted by the agency.

According to Jonathan Adkins, executive director of the Governors Highway Safety Association, which represents state highway safety organisations, “Another day, another Tesla problem. It’s encouraging to see the National Highway Traffic Safety Administration (NHTSA) taking a more active role in reining in this firm.”

Tesla recalled roughly 12,000 U.S. vehicles sold since 2017 November due to a communication problem that could result in a false forward-collision warning or sudden emergency brake activation.

The recall came after NHTSA in October asked Tesla why it had not issued a recall to address software updates made to its Autopilot driver-assistance system to improve the vehicles’ ability to detect emergency vehicles.

Last week, Tesla recalled 578,607 U.S. vehicles because pedestrians may not be able to hear a required warning sound of an approaching car due to loud music or other sounds played by its “Boombox” feature.

Musk said last week on Twitter “the fun police made us do it (sigh).”