"We will go through the difficult process of reducing our global workforce on Friday," Twitter said in the email.
"We recognise 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.
The company said office access would be immediately limited "to help ensure the safety of each employee as well as Twitter systems and customer data".
All staff are set to receive an email with the subject "Your Role at Twitter" by 09:00 Pacific time (16:00 GMT) on Friday.
Workers who are not affected will be notified through their company email, according to Twitter.
Meanwhile, those who are affected will be told of the "next steps" through their personal accounts.
"Given the nature of our distributed workforce and our desire to inform impacted individuals as quickly as possible, communications for this process will take place via email," Twitter said.
"Exodus of talent"
There is speculation that as many as half of Twitter's 8,000 jobs are on the chopping block.
The platform struggles to make a profit. One way to fix the problem is by making a dent in the wage bill.
Simon Balmain, a senior community manager for Twitter in the UK, told the BBC that he believed he has been laid off, because he was logged out of his work laptop and Slack messaging programme.
"Everyone got an email saying that there was going to be a large reduction in headcount, and then around an hour later, folks started getting their laptops remotely wiped and access to Slack and Gmail revoked," he said.
"Most UK folks are probably asleep and don't know yet. I was working mostly LA (Los Angeles) hours because of the projects I was on, so was still awake when it happened."
Another Twitter worker said he was anxiously waiting for an email to arrive, confirming whether he still had a job.
He said he would probably stay up late to wait for the message.
"The exodus of talent from this lay-off will reshape the whole technology industry as we know it. We're all looking out for each other and the outreach of love and support has been incredible to see," Mr Balmain said.
Bloomberg, citing unnamed sources, suggested some senior staff were asked to make lists of employees to be cut on their teams.
Cryptocurrency platform Binance invested in Twitter as part of Mr Musk's takeover. Earlier, Changpeng Zhao, its chief executive, said that "a slimmer workforce would make more sense".
Mr Zhao, who was speaking at the Web Summit in Lisbon, also criticised the platform for having been slow to roll out new features, given its level of staffing.
Pay to verify
The cost-cutting follows criticism of Twitter's efforts to raise money by proposing to charge $8 (£7) a month for a "verified" blue check-mark.
In addition to the verification badge, those who pay could have their tweets promoted more widely and see fewer adverts.
Mr Musk has tweeted of his plan: "We need to pay the bills somehow."
Twitter has not made a profit in several years and its number of users has remained fairly static at about 300 million a month.
Many experts suggest that Mr Musk, the world's richest man, overpaid for the company, given current economic conditions and the depressed values of many tech stocks.
But Brandon Borrman, Twitter's former head of global communications, in a BBC interview, questioned how Twitter could justify asking people to pay in order to remain on an "equal playing field" with other users.
It is not clear how the cuts will affect the platform's operations. Mr Musk has a reputation for being ruthless when it comes to staff.
US media reports already speak of long hours spent by some staff to meet Mr Musk's demands in the aftermath of the takeover.
In May, Mr Musk said his work ethic expectations would be "extreme", but less than he demanded of himself.