Twitter CEO Elon Musk early Wednesday issued the social media platform's staff an ultimatum, asking them choose between working "long hours" or losing their jobs.

In a company email, the Tesla (TSLA) CEO called on employees to buy in to his "Twitter 2.0" vision. The move comes after Musk laid off key leadership, fired nearly 3,700 full-time employees, and eliminated several contractors without notice. Musk has also fired several Twitter engineers who criticized him on the site and in internal Slack channels.

"Going forward, to build a breakthrough Twitter 2.0 and succeed in an increasingly competitive world, we will need to be extremely hardcore. This will mean working long hours at high intensity. Only exceptional performance will constitute a passing grade," he wrote in an email obtained by CNBC.

Since taking over Twitter in late October, Musk has initiated a number of changes and suggested new features for the site, including a revamped verification system. As part of the $8-a-month Twitter Blue subscription, users would get a blue tick that's identical to the existing verification, which indicate whether accounts are authentic and official.

After a series of high-profile imposter accounts were verified, the company killed the service. In one case, a fake account posing as the pharmaceutical company Eli Lilly, shared a tweet about insulin being free. Out-of-pocket insulin costs averaged $572 in 2020, according to the Kaiser Family Foundation.

The tweet last week sank the firm's stock nearly 4%, wiping a sizeable chunk of its market cap. The company joined other major firms in suspending advertising on the platform.

In another case, a Washington Post reporter was able to create an account impersonating Sen. Ed Markey (D-Mass.) and get verified under the Blue service, prompting Markey to issue a warning to Musk and Twitter.

"I'm asking for answers from [Elon Musk] who is putting profits over people and his debt over stopping disinformation," Markey wrote in a tweet.

Musk has said he is keen to delay a new rollout of Twitter Blue to Nov. 29.

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