Tesla Inc. was admonished by a US agency over how the carmaker was promoting its driver-assistance technology on social media months before the regulator opened a defect investigation of the system.

In a May 15 email sent to Tesla representatives, a National Highway Traffic Safety Administration official flagged seven social media posts the company had shared that gave the agency pause. Each post on X, the service that Tesla Chief Executive Officer Elon Musk owns, showcased disengaged drivers using the system Tesla has marketed as Full Self-Driving, or FSD.