(CNN) — Twitter’s new owner Elon Musk has given employees until Thursday evening to commit to “extremely hardcore” work or else leave the company, according to a copy of a late-night internal email sent by the billionaire and obtained by CNN.

“Going forward, to build a breakthrough Twitter 2.0 and succeed in an increasingly competitive world, we will need to be extremely hardcore,” Musk wrote in the memo. “This will mean working long hours at high intensity. Only exceptional performance will constitute a passing grade.”

In the memo, Musk goes on to outline how Twitter will be “much more engineering-driven” and then gives staff an ultimatum. “If you are sure that you want to be part of the new Twitter, please click yes on the link below,” directing staff to what appears to be an online form.

Musk said any employee who has not done so by 5 p.m. ET on Thursday will receive three months severance. The Washington Post was first to report the memo.

The email, with the subject line “A fork in the road,” comes as Musk has publicly and privately clashed with Twitter employees over his approach to running the company. It also comes after Musk pushed out Twitter’s top execs, eliminated the board of directors and laid off roughly half the staff.

“Whatever decision you make,” Musk said in the memo, “thank you for your efforts to make Twitter successful.”

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