• Elon Musk's ultimatum for Twitter workers did not go to plan.

• Several hundred workers and some entire departments resigned on Thursday.

• One department hit with a large wave of resignations is finance, including payroll.

A large portion of Twitter's financial organization, including its payroll department, left the company on Thursday in response to an ultimatum from Elon Musk that has seemingly backfired.

Along with the payroll department resigning, Twitter's US Tax team and its financial reporting team also resigned, two people familiar with the matter said, matching several internal messages seen by Insider. All three segments of the company were part of Twitter's finance and accounting organization. While accounting was "less impacted" by resignations on Thursday, that part of the organization is smaller now, too, one of the people said.

Employees are set to get paid again next week, one former worker said. While those payments are likely to have been already approved, the next round of payments will not have been, the person said.

"What happens in another two weeks?" the person asked. "When everyone who can approve something is gone."

"Now we'll never see our money," another former employee said. All the people who spoke with Insider asked not to be identified discussing sensitive matters. An email seeking comment from Twitter last night was not returned.

The loss of payroll and other financial department employees happened as part of a mass resignation of Twitter workers who refused to sign up for Musk's proposed "Twitter 2.0." In a Tuesday email, the billionaire, who took over Twitter about three weeks ago, said the platform would now be an "extremely hardcore" and engineering forward place to work. He told the entire company to decide by Thursday at 5 pm ET if they wanted to continue working at this version of Twitter. Those who did were to click a link included in the email. Those who did not click the link, which only had a "yes" option, would be considered to have decided to be part of a voluntary layoff and would receive three months of pay as severance, Musk said.