A Meta whistleblower told US senators on Wednesday that the company undermined national security in order to build a $18 billion business in China.

At a congressional hearing, Sarah Wynn-Williams, a former global public policy director at Facebook, said she watched as executives decided to provide the Chinese Communist Party‬ with access to the data of Meta users, including that of Americans.

Meta has disputed Ms Wynn-Williams's statements.

"Sarah Wynn-Williams' testimony is divorced from reality and riddled with false claims," said Meta spokesman Ryan Daniels.

Mr Daniels said CEO Mark Zuckerberg has been public about the company's interest in offering its services in China, but added. "[T]he fact is this: we do not operate our services in China today."

Meta does, however, generate advertising revenue from advertisers based in China.

During her testimony before a Senate judiciary subcommittee, Ms Wynn-Williams also alleged the parent company of Facebook and Instagram worked "hand in glove" with Beijing to build censorship tools aimed at silencing critics of the Chinese Communist Party.

Specifically, she said Meta capitulated to China's demands that it delete the Facebook account of Guo Wengui, a Chinese dissident living in the US.

Meta maintains it has unpublished Mr Guo's page and suspended his profile because it violated the company's Community Standards.

"One thing the Chinese Communist Party and Mark Zuckerberg share is that they want to silence their critics. I can say that from personal experience," Ms Wynn-Williams said during her testimony.

In March, Ms Wynn-Williams released a memoir called "Careless People" about her experience at the company, which was then called Facebook.

Meta won an emergency ruling in the US that temporarily blocked her from promoting her book, which included several critical claims about her time at the company.

"[T]he false and defamatory book should never have been published," Meta said at the time.

Wednesday's hearing before members of the US Senate was led by Senator Josh Hawley, a Republican from Missouri.

Sen Hawley opened the hearing by saying Meta had "stopped at absolutely nothing to prevent" Wednesday's testimony by Ms Wynn-Williams, who joins Frances Haugen and Arturo Béjar as former employees who have spoken out against the social media giant.

"Why is it that Facebook is so desperate to prevent this witness from telling what she knows?" Hawley said.

At a fiery January 2024 congressional hearing at which Mr Zuckerberg also testified, Sen Hawley demanded that the CEO apologise to families who said their children had been harmed by social media.

Behind Mr Zuckerberg at the 2024 hearing sat a row of families who said their children had self-harmed or killed themselves as a result of social media content.

Mr Zuckerberg turned and told families in the audience that "no one should go through" what they had.

During Wednesday's hearing, Sen Hawley said Meta had suggested Ms Wynn-Williams could face financial penalties for speaking out.

"They have threatened her with $50,000 in punitive damages every time she mentions Facebook in public, even if the statements that she is making are true," Sen Hawley alleged. "Even as we sit here today, Facebook is attempting her total and complete financial ruin."

On Wednesday, the company told the BBC the $50,000 in damages is for each material violation of the separation agreement that she signed when she departed the company in 2017.

Ms Wynn-Williams says Meta told her that creating exceptions to the non-disparagement agreement would "eat the rule," which Meta later clarified to the BBC was the comment of an arbitrator, not the company.

The company added that she was not restricted from testifying before Congress.

But Meta declined to directly respond to a BBC inquiry about whether Ms Wynn-Williams may indeed face financial penalties initiated by the company or its lawyers for statements she made on Wednesday in front of Congress.

Ms Wynn-Williams told lawmakers that all of this had taken a personal toll on her.

"The last four weeks have been very difficult," she told members of the Senate committee. "Even the choice to come and speak to Congress is incredibly difficult."