Elon Musk has fired a group of Twitter engineers, some of whom posted critical comments either on the social network or on its internal Slack messaging system, according to two current Twitter employees and one former employee familiar with the situation.

NBC News could not confirm exactly how many employees had been let go in the latest firings, but one person familiar with the situation estimated it could be as high as 20. The people asked to withhold their names out of concern of professional consequences and fears of retaliation.

Some of the newly fired engineers spoke out on Twitter, others in a widely accessible internal Slack channel called “social watercooler.”

Musk had already tweeted Monday that he had fired at least one engineer who publicly criticized him on Twitter.

The latest terminations come in the wake of Musk’s decision to let go of about half of all Twitter employees in a bid to cut costs.

Some Twitter employees confirmed the firings on their verified accounts.

"Looks like I just got fired for s---posting too," one wrote in response to another person who said they had been let go.

One ex-Twitter employee, who was laid off in the first major round of layoffs two weeks ago, said the latest firing emails were sent around 4:30 a.m. ET Tuesday to “anyone who snarkposted about [Musk] in one of the company Slack channels or on Twitter in the last 24 hours.”

Many ex-Twitter employees now regularly communicate with current employees through private chat groups outside of the company’s Slack, sharing screenshots of recent dictums and infighting from Musk’s teams, some of which have been shared with NBC News.

"I can’t begin to describe the institutional knowledge they’re taking with them," a current employee said. "These were the ones considered too important to cut during layoffs."

Another current employee said that they received guidance from their manager to be careful about speaking about any mistakes Twitter makes under Musk.

Musk completed his acquisition of Twitter for $44 billion last month, and soon after revealed the company was losing money at a torrid clip and could even face bankruptcy. An attempt to begin charging users $7.99 for a blue checkmark quickly backfired after users began purchasing them only to impersonate official accounts.

On Tuesday, a half-dozen of the platform's engineers tweeted that they had been let go after criticizing Musk's decision-making, with some showing emails from the company citing "recent behavior" as the reason.

The former employee said some of the engineers had been locked out of the company's systems without formally being notified of their termination.

Twitter and Musk did not respond to requests for comment.

Later on Tuesday, Musk appeared to confirm the firings.

"I would like to apologize for firing these geniuses," he wrote on Twitter. "Their immense talent will no doubt be of great use elsewhere."