Elon Musk has given Twitter’s remaining employees until Thursday evening to decide whether they want to remain at the company, saying those who do not want to be a part of the “new Twitter” will be let go.

In an email sent to staff, the billionaire said employees will need to be “extremely hardcore” to build a “breakthrough Twitter 2.0” and said it will mean “working long hours at high intensity”.

The new Twitter owner has been criticised over his treatment of staff since his 44-billion-dollar takeover last month – most notably for laying off around half of Twitter’s 7,500 staff by email as part of cost-cutting measures and firing more staff in recent days who reportedly questioned his approach on employee message boards.

Elon Musk buys Twitter
Critics of Elon Musk have suggested the removal of staff who disagree with his opinions contradicts his claim that he strongly supports free speech (Yui Mok/PA)

His latest email asked Twitter staff to “click yes” on a form included in an email if they “want to be part of the new Twitter”.

“Anyone who has not done so by 5pm ET tomorrow (Thursday) will recieve three months of severance,” the email said.

Alongside the warning about longer, more intense working hours, the message said that “only exceptional performance will constitute a passing grade”.

Trade union Prospect said the email had also been sent to Twitter UK employees and criticised Mr Musk’s approach, saying that it “flies in the face of how both changes to employees’ terms and conditions, and redundancies, should be done in this country.”

It comes after a number of Twitter staff were reportedly fired for criticising Elon Musk on internal employee message boards.

As many as 20 employees have been told that their behaviour violated company policy and that their employment was being terminated immediately.

According to reports in the US, a number of staff had criticised or questioned Mr Musk’s recent tweets about the Twitter app’s “slow” performance on Slack, a messaging platform used officially by staff inside Twitter.

Earlier this week, a Twitter engineer who publicly disagreed with the billionaire’s tweets was said to have been laid off, with Mr Musk tweeting “he’s fired”.

Mr Musk even appeared to mock those staff who were fired, tweeting in reply to a link to the story: “I would like to apologize for firing these geniuses. Their immense talent will no doubt be of great use elsewhere.”

Critics of the Tesla and SpaceX boss have suggested the removal of staff who disagree with his opinions contradicts his claim that he strongly supports free speech and wants to allow more of it on Twitter.

The latest incidents continue a tumultuous first few weeks in charge for Mr Musk, who has laid off half of Twitter’s workforce only to now be seeking to rehire some of them to plug staffing gaps.

Elon Musk
Elon Musk (Evan Agostini/Invision/AP)

The company’s attempt to introduce a new version of its Twitter Blue subscription package – giving users a verified blue tick badge if they pay £6.99 a month – has also been mired in confusion after it was launched, only to be pulled barely a day later.

New grey “Official” badges to identify authentic, verified accounts have also been rolled out, taken down and then launched again in recent days, further adding to the confusion around the platform’s future.

Mr Musk has said Twitter needs more subscriptions to boost revenue and told staff last week that the collapse of the company was not out of the question if changes were not made.

Some safety experts have raised concerns that giving a verified account badge to any account willing to pay for it will help bad actors spread misinformation.

The Twitter boss has now said the relaunch of the Blue subscription has been pushed back until the end of the month “to make sure that it is rock solid”.