Elon Musk warned Twitter employees Thursday to brace for 鈥渄ifficult times ahead鈥 that might end with the collapse of the social media platform if they can't find new ways of making money.

Workers who survived last week's mass layoffs are facing harsher work conditions and growing uncertainty about their ability to keep Twitter running safely as it continues to lose high-level leaders responsible for data privacy, cybersecurity and complying with regulations.

That includes Yoel Roth, Twitter鈥檚 head of trust and safety 鈥 a previously little-known executive who became the public face of Twitter鈥檚 content moderation after Musk took over and who had been praised by Musk for defending Twitter鈥檚 ongoing efforts to fight harmful misinformation and hate speech. An executive confirmed Roth鈥檚 resignation to coworkers on an internal messaging board seen by The Associated Press.

The developments were part of another whirlwind day in Musk's acquisition of the social media platform. It began with an email to employees from Musk on Wednesday night ordering workers to stop working from home and show up in the office Thursday morning. He called his first 鈥渁ll-hands" meeting Thursday afternoon. Before that, many were relying on the billionaire Tesla CEO's public tweets for clues about Twitter's future.

鈥淪orry that this is my first email to the whole company, but there is no way to sugarcoat the message," wrote Musk, before he described a dire economic climate for businesses like Twitter that rely almost entirely on advertising to make money.

鈥淲ithout significant subscription revenue, there is a good chance Twitter will not survive the upcoming economic downturn,鈥 Musk said. 鈥淲e need roughly half of our revenue to be subscription.鈥

At the staff meeting, Musk said some 鈥渆xceptional鈥 employees could seek an exemption from his return-to-office order but that others who didn鈥檛 like it could quit, according to an employee at the meeting who spoke on condition of anonymity out of a concern for job security.

The employee also said Musk appeared to downplay employee concerns about how a pared-back Twitter workforce was handling its obligations to maintain privacy and data security standards, saying as CEO of Tesla he knew how that worked.

Musk鈥檚 memo and staff meeting echoed a livestreamed conversation trying to assuage major advertisers Wednesday, his most expansive public comments about Twitter鈥檚 direction since he closed a US$44 billion deal to buy the social media platform late last month and dismissed its top executives. A number of well-known brands have paused advertising on Twitter.

Musk told employees the 鈥減riority over the past 10 days" was to develop and launch Twitter's new subscription service for $7.99 a month that includes a blue check mark next to the name of paid members 鈥 the mark was previously only for verified accounts. Musk's project has had a rocky rollout with an onslaught of newly bought fake accounts this week impersonating high-profile figures such as basketball star LeBron James and the drug company Eli Lilly to post false information or offensive jokes.

In a second email to employees, Musk said the 鈥渁bsolute top priority" over the coming days is to suspend 鈥渂ots/trolls/spam鈥 exploiting the verified accounts. But Twitter now employs far fewer people to help him do that.

An executive last week said Twitter was cutting roughly 50 per cent of its workforce, which numbered 7,500 earlier this year.

Musk told employees in the email that 鈥渞emote work is no longer allowed" and the road ahead is 鈥渁rduous and will require intense work to succeed," and that they will need to be in the office at least 40 hours per week.

Twitter's ongoing exodus includes the company's chief privacy officer, Damien Kieran, and chief information security officer Lea Kissner, who tweeted Thursday that 鈥淚鈥檝e made the hard decision to leave Twitter.鈥

Roth鈥檚 resignation is a 鈥渉uge loss鈥 for Twitter鈥檚 reliability and integrity, said his former coworker and friend Emily Horne.

鈥淗e鈥檚 worked incredibly hard under very challenging circumstances, including being personally targeted by some of the most vicious trolls who were active on the platform,鈥 said Horne, who oversaw global policy communications at Twitter until 2018. 鈥淗e stayed through all of that because he believed so deeply in the work his team was doing to promote a public conversation and improve the health of that conversation."

Cybersecurity expert Alex Stamos, a former Facebook security chief, tweeted Thursday that there is a 鈥渟erious risk of a breach with drastically reduced staff鈥 that could also put Twitter at odds with a 2011 order from the Federal Trade Commission that required it to address serious data security lapses.

鈥淭witter made huge strides towards a more rational internal security model and backsliding will put them in trouble with the FTC鈥 and other regulators in the U.S. and Europe, Stamos said.

The FTC said in a statement Thursday that it is 鈥渢racking recent developments at Twitter with deep concern."

鈥淣o CEO or company is above the law, and companies must follow our consent decrees," said the agency's statement. 鈥淥ur revised consent order gives us new tools to ensure compliance, and we are prepared to use them.鈥

The FTC would not say whether it was investigating Twitter for potential violations. If it were, it is empowered to demand documents and depose employees.

In an email to employees seen by the AP, Musk said "Twitter will do whatever it takes to adhere to both the letter and spirit of the FTC consent decree.鈥

鈥淎nything you read to the contrary is absolutely false. The same goes for any other government regulatory matters where Twitter operates," Musk wrote.

Twitter paid a $150 million penalty in May for violating the 2011 consent order and its updated version established new procedures requiring the company to implement an enhanced privacy protection program as well as beefing up info security.

Those new procedures include an exhaustive list of disclosures Twitter must make to the FTC when introducing new products and services 鈥 particularly when they affect personal data collected on users.

Musk is fundamentally overhauling the platform's offerings and it's not known if he is telling the FTC about it. Twitter, which gutted its communications department, didn't respond to a request for comment Thursday.

Musk has a history of tangling with regulators. 鈥淚 do not respect the SEC,鈥 Musk declared in a 2018 tweet.

The Securities and Exchange Commission recently examined for possible tardiness his disclosures to the agency of his purchases of Twitter stock to amass a major stake. In 2018, Musk and Tesla each agreed to pay $20 million in fines over Musk鈥檚 allegedly misleading tweets saying he鈥檇 secured the funding to take the electric car maker private for $420 a share. Musk has fought the SEC in court over compliance with the agreement.

The consequences for not meeting FTC's requirements can be severe 鈥 such as when Facebook had to pay $5 billion for privacy violations.

鈥淚f Twitter so much as sneezes, it has to do a privacy review beforehand,鈥 tweeted Riana Pfefferkorn, a Stanford University researcher who said she previously provided Twitter outside legal counsel. 鈥淭here are periodic outside audits, and the FTC can monitor compliance.鈥

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AP reporters Frank Bajak and Marcy Gordon contributed to this report.