When Twitter reopened offices in March, it had said employees could still work from home if they wanted.
But Musk's new move at the social media platform reflects policies at his other companies, SpaceX and Tesla Inc. where he told employees to work in the office at least 40 hours a week, or leave.
Musk, who completed his $44 billion deal for Twitter just two weeks ago, has laid off half its workforce and several top executives and announced a series of actions including charging $8 for the Twitter Blue subscription.
Musk also told employees that he wants to see subscriptions account for half of Twitter's revenue, the report said, citing the email.
The company did not immediately respond to a Reuters request for comment.