Complaints filed with the National Highway Traffic Safety Administration (NHTSA) of incidences of Tesla vehicles braking unexpectedly and unnecessarily are mounting and the regulator says it’s looking into it.

“Phantom braking,” as the phenomenon is often called, is an unsettling and potentially dangerous fault in vehicles equipped with advanced driver assistance systems that causes them to misinterpret what’s happening on the road and slam on the brakes. Naturally, it’s a hazard for other vehicles behind it and has been a persistent issue in Teslas.

According to The Washington Post, reports of phantom braking have risen to 107 in the last three months, compared to just 34 in the preceding 22 months. The timing coincides with Tesla’s decision to stop using radar sensors in its vehicles in favor of a camera-only system.

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The move, along with a recall, was supposed to curb incidences of phantom braking but has been widely criticized by experts in the driver assistance field.

“Phantom braking is what happens when the developers do not set the decision threshold properly for deciding when something is there versus a false alarm,” Phil Koopman, a Carnegie Mellon University professor who focuses on autonomous vehicle safety told The Washington Post. “What other companies do is they use multiple different sensors and they cross-check between them – not only multiple cameras but multiple types of sensors.”

A bag floating across a road, for instance, may look like a truck to a camera, but if it can be corroborated with radar or LiDAR, a phantom braking scenario may be avoided.

Now, the NHTSA has said that it is aware of the complaints and is reviewing them. It is also in discussions with Tesla and is reviewing additional data sources. The regulator has put Tesla under increased scrutiny of late and is investigating accidents related to its advanced driver assistance systems.

Drivers, meanwhile, have been calling these phantom braking events “hair raising” and potentially “disastrous.”