Tesla said it received a subpoena from the US securities regulator related to a settlement that required CEO Elon Musk's tweets on material information about the company to be vetted.

source https://gadgets.ndtv.com/transportation/news/tesla-elon-musk-twitter-tweet-vet-subpoena-us-sec-regulator-2018-settlement-2755435#rss-gadgets-all