The National Highway Traffic Safety Administration (NHTSA) sent Elon Musk a cease-and-desist letter last October over “misleading statements” Tesla made about the Model 3’s safety. The agency also asked the Federal Trade Commission to investigate whether the statements “constitute[d] unfair or deceptive acts or practices.”

The letter and the referral were made public in documents acquired via a Freedom of Information Act (FOIA) request by legal nonprofit Plainsite.org. The FOIA documents show that the NHTSA issued multiple subpoenas to Tesla following high-profile crashes involving the company’s cars. They also show that Tesla has met with the NHTSA on a quarterly basis to keep the agency updated on topics like Autopilot and over-the-air software updates, review crashes, and to give the regulators test rides in the company’s cars.

The NHTSA specifically took issue with an October 2018 blog post in which Tesla claimed that the Model 3 had “the lowest probability of injury of any vehicle ever tested by” the federal safety agency. Comparing the NHTSA’s frontal crash ratings or overall safety scores of two cars with more than 250 pounds in weight difference is “inappropriate,” the agency wrote in its letter to Musk. As an example, the agency pointed out that if a Model 3 crashed headlong into a significantly heavier SUV, the SUV would have a greater chance of “survivability and injury avoidance,” regardless of the Model 3’s frontal crash rating.

Tesla says the Model 3 has “the lowest probability of injury”

“It is therefore inaccurate to claim that the Model 3 has ‘the lowest probability of injury of all cars,’ or that Model 3 occupants are ‘less likely to get seriously hurt,’ or ‘have the best chance of avoiding a serious injury,’” the agency wrote. Tesla’s blog post, it said, “could be interpreted as misunderstanding safety data, an intention to mislead the public, or both.”

The NHTSA released a blog post of its own last October, two days after Tesla’s, in which the agency said “there is no ‘safest’ vehicle among those vehicles achieving 5-star ratings,” though it didn’t mention the automaker by name.

Tesla’s deputy general counsel Al Prescott argued in a response to the agency that it’s “incorrect” to assert that the company didn’t comply with the NHTSA’s guidelines. He said Tesla pulled publicly available data from the NHTSA to make its own calculations about crash probability. “We had hoped NHTSA would welcome such an achievement because it was presented in an objective manner using the agency’s own data,” Prescott wrote. Tesla “provided consumers with fair and objective information to compare the relative safety of vehicles having 5-star overall ratings,” he said.

Tesla declined to comment beyond Prescott’s response to the NHTSA. Representatives for the NHTSA and the FTC did not immediately respond to requests for comment.

The NHTSA asked the FTC to investigate Tesla’s claims

Tesla previously ran afoul of the agency’s safety rating guidelines in 2013 when it claimed that the Model S had achieved a “new combined record of 5.4 stars” — despite the fact that the NHTSA only issues safety ratings of up to 5 stars. In response, the NHTSA rewrote its guidelines, leaving less wiggle room for automakers to play with the safety numbers.

The October 2018 blog post, then, was a repeat offense in the eyes of the NHTSA, which is why the agency asked the FTC to investigate whether Tesla’s statements. Breaking with the guidelines, the NHTSA said in its letter to Musk, could cause consumer confusion and “give Tesla an unfair market advantage.”

(The NHTSA has also poured cold water on a statistic Tesla has often used to describe the relative safety of Autopilot.)

Other documents in Plainsite.org’s FOIA cache offer more detail about how closely the NHTSA has followed a number of high-profile crashes that involved Tesla’s cars, including a fatal crash on March 1st of this year where the driver was using Autopilot. (The family of this driver sued Tesla last week.) The agency subpoenaed Tesla for things like the vehicle data logs from the cars in these crashes, and the automaker complied with the subpoenas (though with a few redaction requests).