As the damning details of Facebook’s largest-ever data breach at the hands of pro-Trump data firm Cambridge Analytica continue to pour in—and as the social media giant’s share price continues to plummet as a result—Sen. Richard Blumenthal (D-Conn.) on Monday called on CEO Mark Zuckerberg to “testify under oath” before Congress to explain why his company took so long to notify users that their information had been compromised.

“Zuckerberg ought to be subpoenaed to testify if he won’t do it voluntarily.”
—Sen. Richard Blumenthal”Zuckerberg ought to be subpoenaed to testify if he won’t do it voluntarily,” Blumenthal, a member of the Senate Judiciary Committee, told reporters late Monday, echoing demands of other lawmakers. “He owes it to the American people who ought to be deeply disappointed by the conflicting and disparate explanations that have been offered.”

Blumenthal’s request comes amid growing calls—both in the U.S. and overseas—for Zuckerberg to answer for his company’s failure to ban Cambridge Analytica in 2015, when the platform first discovered that the personal information of millions had been harvested in violation of company policy.

Since details of Cambridge Analytica’s exploitation of Facebook were published by the New York Times and the Observer over the weekend, the social media giant has downplayed the incident, argued that it doesn’t constitute a data breach at all, and maintained that Cambridge Analytica is solely to blame for the improper harvesting of personal data.

But privacy advocates have argued that while Cambridge Analytica should be held accountable for its actions, Facebook cannot be let off the hook.