A former Twitter Inc executive turned whistleblower is set to testify on Tuesday before a U.S. Senate committee about his claims of serious security lapses at the social media network.

A deadline for Twitter shareholders to vote on Elon Musk's deal to buy the company also falls on Tuesday.

The testimony of Peiter "Mudge" Zatko, a famed hacker who served as Twitter's head of security until his firing last year, comes as Twitter and Musk head to trial next month over whether the $44 billion deal should be completed.

The San Francisco-based company sued Musk for terminating the agreement, while the Tesla chief executive countersued, accusing Twitter of misrepresenting the number of false and spam accounts on its service.

A Delaware judge ruled last week that Musk may include Zatko's whistleblower claims in his case against Twitter, but denied his request to delay the trial.

On Tuesday, the Senate Judiciary Committee is expected to question Zatko on his claims that Twitter misled regulators about its compliance with a 2011 settlement with the Federal Trade Commission over improper handling of user data.

Since then, Twitter has made "little meaningful progress on basic security, integrity and privacy systems," Zatko's complaint filed with regulators in July said.

The committee, chaired by U.S. Senator Dick Durban, is also expected to press Zatko on his allegation that one or more of Twitter's employees worked on behalf of foreign governments.

Durbin, speaking to reporters on Monday, said Zatko's claims were "a matter of grave personal and privacy concern."

Twitter has said Zatko was fired for "ineffective leadership and poor performance," and that his allegations appeared designed to harm Twitter.

Zatko's whistleblower complaint appeared to contain over two pages of links to supporting documents, such as emails between Zatko and Twitter CEO Parag Agrawal and an assessment of misinformation and disinformation on Twitter. The number of documents was limited compared to Facebook whistleblower Frances Haugen, who released thousands of pages of internal material.

A majority of Twitter shareholders have voted to approve the takeover by Musk, sources told Reuters on Monday. The company will announce the results during a special meeting on Tuesday.

(Reporting by Sheila Dang in Dallas; additional reporting by Richard Cowan in Washington; Editing by Cynthia Osterman and Nick Zieminski)