US highway safety regulators are investigating an apparent hidden feature in Tesla’s Autopilot software that can reportedly disable the safety prompts Tesla gives to drivers to keep their hands on the steering wheel. The regulators are demanding information from the automaker about whether consumers could try to circumvent the safety controls on Tesla’s driver-assist technology.

In a letter to Tesla dated July 26 and made public by the National Highway Traffic Safety Administration this week, US authorities expressed concern that the recent discovery of the setting — which has since been widely and unofficially dubbed “Elon mode” — could encourage unsafe driving behavior.

“NHTSA is concerned that this feature was introduced to consumer vehicles and, now that the existence of this feature is known to the public, more drivers may attempt to activate it,” wrote NHTSA Acting Chief Counsel John Donaldson in the letter. “The resulting relaxation of controls designed to ensure that the driver remain engaged in the dynamic driving task could lead to greater driver inattention and failure of the driver to properly supervise Autopilot.”

The letter was first reported by Bloomberg. NHTSA’s demand for information comes after a user on X, the platform formerly known as Twitter, in June claimed to have accessed a non-public setting in Tesla’s software such that it no longer periodically prompts, or “nags,” drivers to apply torque to the steering wheel while Autopilot or Full Self-Driving modes — the company’s more advanced driver-assist package — are active.

The X user later claimed to have performed a 600-mile test drive with the reminders disabled.

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

CNN has not been able to independently verify the X account’s claims or the identity of the account holder. In an email, the user declined to reveal their identity or to walk through how they discovered the Tesla setting.

NHTSA’s letter called on Tesla to provide information including how many of its cars may have the software containing the hidden feature, as well as what it takes to access it and why the company installed it on consumer vehicles in the first place. It also requests records of crashes and near-misses involving Tesla vehicles that had the hidden setting enabled.

The letter set a deadline of Aug. 25 and warned that failure to comply could result in fines of up to more than $26,000 a day.

A subsequent filing released by NHTSA showed that Tesla did respond to the agency’s request for information by the deadline, but that the company requested and received confidential treatment for its report, meaning the information Tesla provided to NHTSA will not be made public.