Tesla Model 3 Silas Stein | picture alliance | Getty Images

The U.S. National Highway Traffic Safety Administration (NHTSA) sent Tesla a letter regarding claims the company made on the safety of its Model 3 sedan. NHTSA Chief Counsel Jonathan Morrison sent Tesla CEO Elon Musk a cease-and-desist letter in October last year to say it had become aware of "misleading statements" made by the company about the vehicle's safety rating. The agency's main contention was with Tesla's claim in a blog post that month that NHTSA tests showed the Model 3 has "the lowest probability of injury of all cars the safety agency has ever tested." The NHTSA said in the letter, which was posted on the legal transparency website PlainSite, that it had also referred the matter to the Federal Trade Commission's Bureau of Consumer Protection.

It said it was "not the first time" Tesla had disregarded NHTSA guidelines "in a manner that may lead to consumer confusion and give Tesla an unfair market advantage." According to the documents posted on PlainSite, which were obtained through a Freedom of Information Act request, the NHTSA also issued subpoenas to Tesla ordering it to produce information on several crashes. The NHTSA did publicly dispute Tesla's claims about car safety after the blog post in question was published. The agency at the time said that there was no "safest" ranking within its five-star ranking system for crash tests. Tesla said in a letter in response to the agency at the time that its blog statements were based on "actual test results and NHTSA's own calculations for determining relative risk of injury and probability of injury."