Tesla Inc. shares fell 7.5 percent in premarket trading on Monday as investors prepared for its chief Elon Musk's proposed sale of about a tenth of his holdings in the electric-car maker following his Twitter poll.

Musk, Tesla's chief executive officer and the world's richest person, tweeted on Saturday that he would offload 10 percent of his stock if users of the social media network approved the proposal.

The electric-vehicle maker's shares were down 6.2 percent at $1,146.43. Shares listed in Frankfurt were down about 7 percent at 989.10 euros.

The Twitter poll asking Musk's followers if he should sell stock garnered more than 3.5 million votes, and 57.9 percent of the people voted "Yes".

Musk had previously said he would have to exercise a large number of stock options in the next three months, which would create a big tax bill. Selling some of his stock could free up funds to pay the taxes.

"I was prepared to accept either outcome," Musk said, after the voting ended. Market participants expected speculators would try to front-run his selling.

As of June 30, Musk's shareholding in Tesla came to about 170.5 million shares and selling 10 percent would amount to close to $21 billion based on Friday's close, according to Reuters calculations.

Including stock options, Musk owns a 23 percent stake in Tesla, the world's most valuable car company.

In the three months to November 4, company insiders at Tesla sold $259.62 million worth of shares, excluding dispositions of indirectly held shares, according to Refinitiv Eikon data.

Musk's straw poll follows a proposal by U.S. Senate Democrats to tax billionaires' stocks and other tradeable assets to help finance President Joe Biden's social spending agenda and fill a loophole that has allowed them to defer capital gains taxes indefinitely.

"The last thing you do when offloading a massive exposure is to reveal your hand," said Chris Weston, head of research at broker Pepperstone in Melbourne.

"The buyers tend to step away when you have an overhang like this, but this is no ordinary story and is Musk's way of getting back at the proposal to tax the elite with gains on unrealized profits."

Tesla breached a trillion dollars in market capitalization last month, becoming the fifth U.S. company to join a club which includes Apple, Microsoft, Amazon and Alphabet.

"The dip isn't going to last too long, because Tesla has had such a phenomenal record of bouncing back from these sort of sell-offs," said David Madden, markets analyst at Equiti Capital in London.

Investors will also be watching for any response from regulators to Musk's Twitter poll. The U.S. Securities and Exchange Commission had ordered Tesla to vet any material public communications Musk made regarding the EV maker, following his 2018 tweet that he had "funding secured" to possibly take Tesla private in a $72 billion transaction.