Tesla CEO Elon Musk sold $930 million in shares to meet tax withholding obligations related to the exercise of stock options, U.S. securities filings showed on Monday.

Musk sold 934,091 shares after exercising options to buy $2.1 billion worth of the stock on Monday. The sale was 'solely to satisfy the reporting person's tax withholding obligations related to the exercise of stock options,' the filings said.

However, Musk has now sold a total of $7.8 billion worth of Tesla stock over the past six trading days, and not all of the sales have cited tax withholding requirements. 

On November 6, Musk posted a Twitter poll asking whether he should sell 10 percent of his stake in the company, which would be worth about $20 billion, and vowed to abide by the results in favor of the sale. 

Tesla shares closed at $1,013.39, an unchanged level from Friday's close. 

Stock options are a form of compensation that allow an employee to purchase shares at a pre-arranged value, known as the strike price, making them more valuable as the market price of the shares rises.

Musk on Monday exercised his option to purchase 2.1 million shares at $6.24 each, and is required to pay the difference between the strike price and fair market value, which is taxed as ordinary income. 

Musk faces an August deadline to exercise options on 23 million shares which were granted in 2012. August is also the deadline to pay taxes associated with the grant.

Yet many of his stock sales through the week do not appear to be connected with his tax withholding requirements.