"In an effort to place Twitter on a healthy path, we will go through the difficult process of reducing our global workforce on Friday," said the email sent on Thursday, seen by Reuters.
And it's by e-mails that Twitter workers will find out if they stay or wind up in the unemployment line.
Those spared get their good news in a company e-mail, while those made redundant find out through their personal mail address.
Some employees tweeted their access to the company's IT system had been blocked and feared whether that suggested they had been laid off.
Twitter said in the email that its offices would be temporarily closed and all badge access suspended in order "to help ensure the safety of each employee as well as Twitter systems and customer data."
The company announcement said that Twitter is going through "an incredibly challenging experience."
"We recognize that this will impact a number of individuals who have made valuable contributions to Twitter, but this action is unfortunately necessary to ensure the company's success moving forward," it added.
A class action lawsuit was filed on Thursday against Twitter by its employees, who argued the company was conducting mass layoffs without providing the required 60-day advance notice, in violation of federal and California law.
The lawsuit also asked the San Francisco federal court to issue an order to restrict Twitter from soliciting employees being laid off to sign documents without informing them of the pendency of the case.
Saddled with the purchase of Twitter, for which Musk has said he overpaid, the tycoon is looking for ways for Twitter to make money -- and fast.
His most recent idea was to charge $8 a month to anyone on Twitter who would receive a blue "verified" badge assuring the public that the account is authentic.
Musk has said he wants to increase Twitter's revenue from $5 billion last year to more than $26 billion in 2028.
Top global companies, including General Mills and Volkswagen, suspended their advertising on Twitter on Thursday as pressure builds on Musk to turn his platform into a successful business.
US auto giant General Motors last week was the first major advertiser to suspend advertising following the takeover.
Officials and civil rights groups have expressed worry that Musk will open the site to uncontrolled hate speech and misinformation as well as reinstate banned accounts, including that of former US president Donald Trump.
This report was prepared with data from Reuters and Agence France-Presse