Elon Musk is monitoring the internal messages sent between Twitter employees to fire people who break the rules, act insubordinate or criticise him.

Almost two dozen people have already been fired as a result after the billionaire’s team reviewed what his staff had sent on the messaging app Slack.

They received an email informing them they were being fired for “violating company policy”.

That’s according to the New York Times, which spoke to an inside source that claimed Musk had an entire team combing through private messages of his staff.

It comes as the world’s richest man took over Twitter three weeks ago in a chaotic $72 billion takeover.

Musk has already aggressively sacked thousands of employees worldwide which so far is about half of Twitter’s workforce.

Musk has even openly mocked firing some of his workers in tweets.

Nick Morgan, a former software engineer at Twitter, posted a screenshot on Tuesday of the midnight email he received from human resources.

The email had the subject headline “Your Role at Twitter”.

“We regret to inform you that your employment is terminated effective immediately,” the email said. “Your recent behaviour has violated company policy.”

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After sacking staff because of their private messages, Musk showed no remorse.

“Elon has fired numerous employees who were critical of him on Twitter and the company’s Slack, according to Protocal,” someone posted on Twitter.

Several hours later, Elon fired back: “I would like to apologise for firing these geniuses. Their immense talent will no doubt be of great use elsewhere.”

Earlier this week, the tech billionaire made a fresh round of headlines by publicly sacking a software developer because they criticised him on social media.

“Btw, I’d like to apologise for Twitter being super slow in many countries,” Musk wrote on Sunday. “App is doing >1000 poorly batched RPCs (remote procedure calls) just to render a home timeline!”

This drew San Diego-based Twitter developer Eric Frohnhoefer out of the woodwork, who revealed he had spent six years working on this problem and Musk – his new boss – was plain wrong.

After a back and forth between Musk and Frohnhoefer, Musk simply tweeted “He’s fired”.

Frohnhoefer then confirmed he had been cut from his role.

Elon Musk this week made a fresh round of headlines by publicly sacking a software developer because they criticised him on social media. Photo / AP

Musk’s tweet about Twitter being “poorly batched” also drew out another software developer who also ended up getting sacked.

Twitter employee Sachee Macaw told Musk it was outrageous to sack his batching team and then complain about poor batching.

Shortly afterwards, she too was fired.

“Lol I just got fired for s**t posting,” she shared to her Twitter followers.

“I said it before and I’ll say it again, kiss my a** Elon.”

After screenshots of her spat was shared online, Elon responded with: “A classic case of adult onset Tourette’s.”

The latest row comes after Musk outraged Twitter employees by axing free lunches.

“He fired 3/4 of the employees. Now he’s planning to starve the rest of them. He’s failure incarnate,” a popular tweet responding to his decision read.

Musk fired back a short time later arguing barely any staff fronted up for lunch anyway.

“Especially bizarre given that almost no one came to the office. Estimated cost

A former employee who claimed she quit Twitter because of Musk, challenged the new CEO on the cost of providing breakfast and lunch for staff.

“This is a lie. I ran this program up until a week ago when I resigned because I didn’t want to work for Elon Musk. For breakfast & lunch we spent $20-$25 a day per person. This enabled employees to work thru lunchtime & mtgs. Attendance was anything from 20-50% in the offices,” she tweeted.

Musk however said the ex-staff member was “false” and the company spent “$13M/year on food service for San Francisco headquarters”.

“Badge in records show peak occupancy was 25%, average occupancy below 10%. There are more people preparing breakfast than eating breakfast. They don’t even bother serving dinner, because there is no one in the building,” he replied.

Musk last week reportedly emailed staff telling them they would be expected to be in the office for at least 40 hours a week.