Elon Musk speaks on stage during the Westworld Featured Session during SXSW at Austin Convention Center on March 10, 2018 in Austin, Texas.

Tesla shares are sinking into bear-market territory, as investors worry the company may not hit a key production milestone.

The stock was recently trading at around $310, which is more than 20 percent below its all-time high of $389.61, set in September 2017. To be in a bear-market territory, a sign of very negative investor sentiment, the shares would need to close at $311.69 or lower.

The continued concerns over Tesla's Model 3 production ramp are likely a key factor behind the decline, CFRA analyst Efraim Levy told CNBC.

"There is a growing consensus that they are going to miss their Model 3 production forecast for the first quarter," he said.

Tesla was not immediately available for comment.

Enthusiasm over the Model 3 had been one of the major factors that drove Tesla shares to its all-time high in 2017. The car represents a major leap for the company, from a niche maker of high-end electric cars to a mass-market automaker.

But the production ramp has been rocky.

Tesla had initially aimed to hit a target of producing 5,000 Model 3 cars a week by the end of 2017 but has had to repeatedly push that goal into the future. When Telsa reported its fourth-quarter results it said it would hit 2,500 cars per week by the end of the first quarter of 2018 and 5,000 cars per week by the end of the second.

CNBC has previously reported that current and former Tesla employees say the company is needing to rework parts and vehicles, furthering delays.

Shareholders will vote Wednesday on whether to approve a new $2.6 billion stock option grant plan for Chairman and CEO Elon Musk. Some major shareholders support the plan, but investment advisory firms Glass Lewis and Institutional Shareholder Services both recommend shareholders reject the proposal.

The accident involving an autonomous Uber car in Tempe, Arizona, might also be a short-term factor, Levy said. The incident might be leading investors to re-evaluate positions in any company making autonomous technology.