HOUSTON — Twitter Inc started a major round of layoffs on Friday, alerting employees of their job status by email after barring the entrances to offices and cutting off workers' access to internal systems overnight.

The move follows 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" as advertisers pulled spending.

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. The groups said on Friday they are escalating their pressure and demanding brands pull their Twitter ads globally.

"In an effort to place Twitter on a healthy path, we will go through the difficult process of reducing our global workforce on Friday," Twitter said in an email to staff on Thursday evening announcing the cuts that came on Friday, which was seen by various news outlets.

In the e-mail, Musk said that Twitter had to "go through the difficult process of reducing (its) global workforce on Friday" and that the move "is unfortunately necessary to ensure the company's success moving forward."

The memo added that “to help ensure the safety” of employees and Twitter’s systems, the company’s offices “will be temporarily closed and all badge access will be suspended." All employees were asked to stay at home on Friday and wait for an update on their employment status regarding their fate at the company.

Since Twitter is now a privately held company, it purportedly does not have to answer to shareholders about the job cuts.

"We recognize that this will impact a number of individuals who have made valuable contributions to Twitter, but this action is unfortunately necessary to ensure the company’s success moving forward," the email continued.

The message concluded by acknowledging that it will be “an incredibly challenging experience to go through” for the workforce. — Agencies