Twitter Inc. laid off half of its workforce on Friday but said cuts were smaller in the team responsible for preventing the spread of misinformation, as advertisers pulled spending amid concerns about content moderation.

Tweets by staff of the social media company said teams responsible for communications, content curation, human rights and machine learning ethics were among those gutted, as were some product and engineering teams.

Workers around the world were shown the door and took to Twitter to vent their frustration or disbelief and say goodbye to one of Silicon Valley's most iconic companies. "Woke up to the news that my time working at Twitter has come to an end. I am heartbroken. I am in denial," said Michele Austin, Twitter's director of public policy for the United States and Canada.

The move caps a week of chaos and uncertainty about the company's future under new owner Elon Musk, the world's richest person, who tweeted on Friday that the service was experiencing a "massive drop in revenue" from the advertiser retreat.

Musk blamed the losses on a coalition of civil rights groups that has been pressing Twitter's top advertisers to take action if he did not protect content moderation – concerns heightened ahead of potential pivotal congressional elections on Tuesday.

After the layoffs, the groups said they were escalating their pressure and demanding brands pull their Twitter ads globally.

"Unfortunately there is no choice when the company is losing over $4M/day," Musk tweeted of the layoffs, adding that everyone affected was offered three months of severance pay.

The company was silent about the depth of the cuts until late in the day, when head of safety and integrity Yoel Roth tweeted confirmation of internal plans, projecting the layoffs would affect about 3,700 people, or 50 percent of the staff.

Among those let go were 784 employees from the company's San Francisco headquarters and 199 in San Jose and Los Angeles, according to filings to California's employment authority.

Roth said the reductions hit about 15 percent of his team, which is responsible for preventing the spread of misinformation and other harmful content, and that the company's "core moderation capabilities" remained in place.

Musk endorsed the safety executive last week, citing his "high integrity" after Roth was called out over tweets critical of former President Donald Trump years earlier.

Musk has promised to restore free speech while preventing Twitter from descending into a "hellscape." But major advertisers have expressed apprehension about his takeover for months.

Brands including General Motors Co. and General Mills Inc. have said they stopped advertising on Twitter while awaiting information about the new direction of the platform.

Musk tweeted that his team had made no changes to content moderation and done "everything we could" to appease the groups. Speaking at an investors conference in New York on Friday, Musk called the activist pressure "an attack on the First Amendment."

Twitter did not respond to a request for comment.

A class action was filed on Thursday against Twitter by several employees, who argued the company was conducting mass layoffs without providing the required 60-day advance notice, in violation of federal and California law, according to Reuters.

The lawsuit asked the San Francisco federal court to issue an order to restrict Twitter from soliciting employees being laid off to sign documents without informing them of the pendency of the case.

(With input from agencies)