After Musk assumed control of Twitter in October 2022, he dismissed Twitter's executive leadership and board, and launched four rounds of broad employee terminations. Musk and Twitter terminated employees without providing information about anticipated changes to the severance plan and without paying the employees the benefits to which they were entitled under the plan, the plaintiffs said.

Related: Severance agreements take another hit: The NLRB General Counsel weighs in

"Musk initially represented to employees that under his leadership Twitter would continue to abide by the severance plan," said Kate Mueting, administrative partner in the law firm Sanford Heisler Sharp, which is representing the plaintiffs. "He apparently made these promises knowing that they were necessary to prevent mass resignations that would have threatened the viability of the merger and the vitality of Twitter itself."

Twitter already has been sued for allegedly failing to pay severance, but those cases involve breach of contract claims and not benefits law. The company has said it has paid ex-employees in full. A pending lawsuit filed last month accuses Twitter of also failing to pay millions of dollars in bonuses it owes to remaining employees. Twitter has said the claims lack merit.

The company also faces a series of other lawsuits stemming from the layoffs that began last year, including claims that it targeted women and workers with disabilities. Twitter has denied wrongdoing in the cases in which it has filed responses.