Tesla Inc Chief Executive Elon Musk has asked employees to return to the office or leave the company, according to an email sent to employees on Tuesday night and seen by Reuters.

"Everyone at Tesla is required to spend a minimum of 40 hours in the office per week," the email said.

"If you don't show up, we will assume you have resigned."

Two Tesla sources confirmed the authenticity of the email reviewed by Reuters. Tesla did not respond to a request for comment.

One of Musk's Twitter followers posted another email that Musk apparently sent to executives asking them to work in the office for at least 40 hours per week or "depart Tesla".

In response to this tweet, the billionaire, who has agreed to take Twitter Inc private in a $44 billion deal, said, "They should pretend to work somewhere else." Musk himself could not be reached for comment.

Some tech workers have been resisting efforts to get them to return to work in California, home to one of Tesla's factories and its engineering base, in the face of a resurgence of coronavirus cases.

In May 2020, Musk reopened a Tesla factory in Fremont, defying that county's lockdown measures to curb the spread of the coronavirus. Tesla reported 440 cases at the factory from May to December 2020, according to Alameda County data obtained by legal information site Plainsite.

Last year, Musk's rocket company SpaceX reported 132 Covid-19 cases at its California headquarters, according to county data.

Tesla joins a wave of companies mandating a return to the office for employees.

While some big employers have embraced voluntary work-from-home policies permanently, others including Alphabet Inc's Google are betting that it is best to push in-person interactions among colleagues.

Twitter CEO Parag Agrawal tweeted in March that Twitter offices would be reopening but employees could still work from home if they preferred.

"Wherever you feel most productive and creative is where you will work and that includes working from home full-time forever," Agrawal said in a tweet dated March 3.