The U.S. auto-safety regulator is investigating Tesla Inc. over customer complaints that the company’s most popular vehicles brake for unexpected reasons, the latest probe related to the electric-vehicle maker’s advanced driver-assistance features.

The National Highway Traffic Safety Administration investigation, revealed Thursday, covers roughly 416,000 Model 3 sedans and Model Y compact sport-utility vehicles from model years 2021 and 2022.

The...

The U.S. auto-safety regulator is investigating Tesla Inc. over customer complaints that the company’s most popular vehicles brake for unexpected reasons, the latest probe related to the electric-vehicle maker’s advanced driver-assistance features.

The National Highway Traffic Safety Administration investigation, revealed Thursday, covers roughly 416,000 Model 3 sedans and Model Y compact sport-utility vehicles from model years 2021 and 2022.

The agency said it has received more than 350 complaints alleging unexpected brake activation, often referred to as “phantom braking.” 

The braking occurs when the vehicle’s advanced driver-assistance features, part of a system called Autopilot, are engaged, the complaints allege.

“Complainants report that the rapid deceleration can occur without warning, at random, and often repeatedly in a single drive cycle,” NHTSA said, noting that it aims to determine the scope and severity of the potential problem. Such probes can lead to recalls.

Tesla didn’t immediately respond to a request for comment.

NHTSA opened a broader investigation into Autopilot last summer after a series of crashes involving Teslas and one or more parked emergency vehicles.

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Write to Rebecca Elliott at rebecca.elliott@wsj.com