Shares of Tesla Inc fell 7 per cent on Friday after Chief Executive Elon Musk mocked the U.S. Securities and Exchange Commission on Twitter and David Einhorn's Greenlight Capital slammed the electric carmaker in its quarterly letter.

Musk stirred nerves about a settlement of his securities fraud lawsuit by calling the SEC the "Shortseller Enrichment Commission" on Twitter, just hours after a federal judge ordered him and the regulator to justify their settlement.

"Just want to that the Shortseller Enrichment Commission is doing incredible work," Musk, a frequent critic of investors betting against the electric car company said in the tweet. "And the name change is so on point!"

In its quarterly letter, Greenlight said its short position on Tesla was its second-biggest winner in the third quarter. The hedge fund said Musk has been deceptive and the carmaker's woes resemble those of Lehman Brothers before its collapse.