According to The New York Times, Elon Musk's pledge to sell 10% of his Tesla shares could be seen as a selfless philanthropic act if he hadn't been already forced to sell the amount.

Musk tweeted “much is made lately of unrealized gains being a means of tax avoidance, so I propose selling 10% of my Tesla stock,” as he polled his more than 62 million Twitter followers, insisting he would do as voters say.

Tesla stocks fell by almost 5% on Monday.

On Sunday, Musk ended the poll after 3.5 million followers voted, disclosing that he is ready to accept either outcome.

The interesting part of Musk's poll is the detail he did not mention to followers. 

Regardless of the poll, Musk may have been required to sell a significant portion of his stock in the near future. He has roughly 23 million stock options, which were granted to him in 2012. Those options have subsequently been vested and their expiration date is August 2022. Most stock awards allow CEOs to avoid paying taxes for years, if not indefinitely if the shares obtained from converting the option are not sold.

However, according to Brian Foley, an executive compensation analyst, Musk's grant is a "ticking time bomb" due to the structure and size of the grant. Musk would have to pay income taxes if he used the grant, which is now valued at little under $30 billion and his tax burden might exceed $10 billion.  

Foley added, "Offhand I can’t think of any way for him to get around paying the tax.”

Furthermore, Musk may need to sell additional shares than required to meet his tax obligation. He holds 17% of Tesla's stock, which is presently valued at almost $200 billion. That implies that his weekend tweets, representing a promise to sell nearly $20 billion in Tesla stock, might destabilize the company's shares, notably as experts believe it is already overpriced. 

What makes matters worse is how difficult it may be for Musk to back down on his pledge. According to a professor at Duke University law school, “In the securities law, the problem is this could be seen as a misrepresentation that was meant to mislead if another shareholder sold on Musk’s tweet.”

If trouble were to arise for Musk, it would not be the first time, as he was entangled in a lawsuit by the Securities and Exchange Commission in 2018 for reporting a Tesla sale that never occurred. He also won a defamation lawsuit after he referred to a man on Twitter who saved children stuck in a Thailand cave as a "pedo guy."