SAN FRANCISCO - Billionaire Elon Musk sent an e-mail to Twitter employees requiring them to pledge to stay with the company, working long hours at “high intensity” during its transformation, or to accept a buyout.

Staff will have to complete the online form by 5pm New York time on Thursday or accept three months’ severance pay.

For Twitter to succeed, “we will need to be extremely hardcore”, Mr Musk said in the e-mail, which was seen by Bloomberg. “Only exceptional performance will constitute a passing grade.”

A representative for Twitter did not immediately respond to a request for comment. The Washington Post reported the memo earlier. The form that Mr Musk wanted employees to complete contained a single question: “Would you like to stay at Twitter?”

“Yes” was the only option to click, before “Submit”. That left workers with a lot of questions about the nature of the agreement. Many of them reached out to lawyers for advice on how to respond, according to people familiar with the matter.

“It’s certainly wrong that he’s requiring them to sign this document because it might give them the appearance that this commitment could waive or override other rights that they might have,” said Mr Peter Romer-Friedman, who heads the civil rights and class actions practice at the law firm Gupta Wessler.

If an employee needed accommodation for a disability or needed to go on medical leave, “you can’t fire them for that”, he said.

“And to me, it seems like that’s what he is promising to do, or at least threatening to do, without addressing those specific situations”, he added.

Mr Musk said in the note that going forward, Twitter will be more dominated by engineers, who make up the majority of remaining employees and have the greatest influence at the company, which he called a “software and servers company” at its heart. Design and product management functions will “still be very important and report to me”, he said.

The billionaire announced plans to fire about 3,700 people in his first week in control of the company . The cuts, which included most of Twitter’s senior management, have upset many of the remaining employees.

Mr Musk’s changes have also led to a lack of communication internally and concerns about product breakdowns and technical outages, according to current and former staff.

Since then, Mr Musk has continued to purge employees who have criticised him, sometimes via Twitter. He testified on Wednesday in Delaware that the lion’s share of his time “for the past few weeks” has been spent at the social-media platform, though he said the “fundamental organisational restructuring” will be completed by the end of next week.

Mr Musk has warned since his US$44 billion (S$60 billion) acquisition in October that Twitter could face bankruptcy if it does not start generating more cash. He has told employees they can expect to work 80-hour weeks and fewer office perks such as free food, and ended the company’s work-from-home policy, with a few exceptions.

The reference to long hours could potentially run afoul of labour laws, said Ms Lisa Bloom, owner of the Bloom Firm in Calabasas, California, who is representing a group of Twitter employees laid off since Mr Musk took over.

“I have already heard from a female manager at Twitter who said, ‘I’ve been at the company for many years. I love my job. I also love my two children. I shouldn’t have to chose between my job and seeing my children at night and on weekends’,” Ms Bloom said.

Meanwhile, Twitter was sued by a former contractor for failing to give proper notice, final pay and to reimburse his expenses.

Mr Francisco Rodriguez was employed by Twitter through PRO Unlimited – also known as Magnit – and fired on Nov 12, along with potentially 4,400 to 5,500 others, according to a complaint filed in a San Francisco federal court on Wednesday. Mr Rodriguez is seeking to represent all those workers in a class-action lawsuit.

“Neither Twitter nor Magnit provided full final pay, benefits and expense reimbursement to these employees on their last day of employment, as required by the California Labour Code. To date, these employees have still not received these full payments,” Mr Rodriguez’s lawyer said.

The failure to give proper notice violates federal law and the California Worker Adjustment and Retraining Notification Act, according to the complaint. The Act generally requires at least 60 days of advance notice for mass layoffs at large companies.

Magnit did not immediately respond to a request for comment. BLOOMBERG