High-profile entrepreneur Elon Musk has told Twitter staff that they must commit to working "long hours at high intensity" or else leave the company, according to reports.
In an e-mail to staff, the social media firm's new owner said workers should agree to the pledge if they wanted to stay.
Those who do not sign up by today will be given three months' severance pay, Mr Musk said.
In his e-mail to staff, Mr Musk stated that Twitter "will need to be extremely hardcore" in order to succeed.
"This will mean working long hours at high intensity. Only exceptional performance will constitute a passing grade," he said.
The world's richest man has already announced half of Twitter's 7,500 staff are being let go, after he bought the company in a £38.7billion deal.
No choice
Mr Musk said he had "no choice" over the cuts as the company was losing more than £3million a day. He has blamed "activist groups pressuring advertisers" for a "massive drop in revenue".
The BBC says a host of top Twitter executives have already stepped down following his purchase of the firm.
Last week, the entrepreneur told Twitter staff that remote working would end. Workers would be expected in the office for at least 40 hours a week.
Mr Musk added that there was "no way to sugar coat the message" that the slowing global economy was going to hit Twitter's advertising revenues.
But tech investor Sarah Kunst said the real reason Twitter is facing difficulties is because Mr Musk's takeover had saddled the company with debt.
His behaviour since the takeover has also led some advertisers to pause their spending, she said.
Pain and uncertainty
"He's now trying to inflict that pain and uncertainty on the employees," she said.
She added that there was a question mark over how enforceable Mr Musk's e-mail about hours to staff really was.
"Can you just send an e-mail to staff, and just unilaterally change their working contract? That remains to be seen."
Dan Ives, a senior equity analyst at Wedbush Securities, said that Twitter's culture had "dramatically changed" with Mr Musk at the helm.
"Elon Musk is not going to be doing candlelight dinners and playing ping pong in Twitter's cafeteria - and this is a shock to the system," he said.
"But he also needs to play nice in the sandbox because if key Twitter engineers and developers leave, this will be a major void in the Twitter ecosystem," he warned. "There's a careful balance ahead for him, in this tightrope act."
FTSE 100
The UK's top share index, the FTSE 100, was down three points at 7,347 shortly after opening this morning, following yesterday's 18-point loss.
Brent crude futures slipped 0.38% to $92.51 a barrel.
Companies reporting today
- Full-year results: Virgin Money UK
- Half-year results: Burberry Group, Investec, Mitie Group