(Reuters) – Tesla (NASDAQ:) Inc shares were down 9% on Monday morning as traders prepared for Elon Musk, Chief Executive Officer’s proposal to sell about a tenth his electric-car manufacturer holdings following his tweet (NYSE:) poll.

Musk, who is the richest man in the world, announced on Saturday via Twitter that he will sell 10% of his stock to those using the social media platform.

More than 3.5 Million votes were cast in a Twitter poll, asking Musk’s fans if they think he should buy stock. 57.9% of those who voted for Musk favored selling stock.

At 0731 GMT, Tesla shares were listed in Frankfurt down 7.9% to 980 euro. The U.S. shares of Tesla are up by 73.2% this year, as compared to a 23.9% rise in the index.

Musk previously stated that he would need to exercise many stock options within the next three month, creating a huge tax bill. The possibility of selling some stock would allow him to free up cash for the tax payments.

Musk stated that he was ready to accept any outcome after the vote ended. Participants in the market expected that speculators would attempt to outrun Musk’s selling.

Based on Friday’s close of business, Musk had approximately 170.5 millions shares in Tesla as of June 30, and selling 10% would be close to $21 Billion.

Musk has a 23% ownership stake in Tesla. This includes stock options. Tesla is the world’s most important car company.

According to Refinitiv Eikon data, Tesla insiders sold $259,62 million in shares during the period from Nov. 4 to Nov. 4.

Musk’s straw vote follows a U.S. Senate Democrats’ proposal to tax billionaires stock and other tradeable assets. It will help fund President Joe Biden and close a loophole that allows them to postpone capital gains taxes for a long time.

Chris Weston from Pepperstone, the head of research in Melbourne said that “the last thing you should do is reveal your hand when offloading massive exposure.”

Musk says that buyers will tend to leave when there is an overhang such as this. However, this isn’t a typical story. Musk wants to get back at his proposal to tax elites with profits not realized.

Late in October, Tesla crossed a trillion in market capitalization. This made it the fifth U.S.-based company to join an exclusive club that includes Alphabet (NASDAQ) as well as Microsoft (NASDAQ), Amazon (NASDAQ), and Alphabet.

Weston said, “I would look for clients who are willing to switch to shorting quite aggressively,” but that hold periods could be extremely short-term.