Tesla shares are down 2.82% to $273.88 in before the bell trade.
Mocking the Securities and Exchange Commission, Muck tweeted shortly after the market close on Thursday, describing the SEC as the "Shortseller Enrichment Commission" before snidely praising it for "doing incredible work".
It comes just days after he settled a case with the regulator alleging he duped investors.
Before the New York bell, Costco Wholesale Corp (NASDAQ:COST) saw shares lose 3.52% to $223.52.
Elon Musk calls the SEC the "Shortseller Enrichment Commission" on Twitter shortly after reaching a deal with the agency to settle a lawsuit over his prior tweets https://t.co/HsnhfCIALa pic.twitter.com/WJchxNUefu— CNN Business (@CNNBusiness) October 5, 2018
It came after the multinational group released its fourth-quarter earnings. Costco reported earnings per share (EPS) of $2.36, which was in line with analysts' estimates.
The company saw $44.41 billion in revenue, which was a tad higher than the $44.27 billion, which was expected by analysts.
Mattress Firm (NASDAQ:MFRM) said Friday, as had been flagged in renent days, that it had filed for Chapter 11 bankruptcy protection so it can take steps to strengthen its balance sheet and reshape its store footprint.
The bed mattress retailer has already filed court motions for approval to reject up to 700 leases. It will begin to close roughly 200 stores in the next few days.
It expects to complete prepackaged restructuring within the next 45 to 60 days, the company said.
Shares are down 0.02% to $64.02.