Mark Zuckerberg is not done answering questions from Congress.

Two months after Zuckerberg testified on Capitol Hill, Facebook's CEO is under renewed scrutiny from lawmakers after Facebook admitted that 60 smartphone manufacturers had previously been given access to user data — including one company flagged by U.S. intelligence.

“He never revealed these data-sharing agreements in our hearing in April,” Sen. Bill Nelson, D-Fla., said on the floor of the U.S. Senate Wednesday afternoon. “As a result, it's hard to know what's true anymore.”

Nelson pointed to Facebook’s deals with Chinese companies Huawei and ZTE as being of particular interest.

“And now we learn that Facebook gave Chinese companies believed to be national security risks access to user data,” Nelson said. “What in the world is next? And what in the world is going to protect Americans' personally identifiable private information?”

Nelson and fellow Senator John Thune, R-S.D., sent Zuckerberg a letter on Tuesday that asked the Facebook CEO for clarity on the nature of its agreements with smartphone manufacturers and what oversight Facebook had on the arrangements.

Also at issue is whether the agreements are a violation of a 2011 Federal Trade Commission Consent Order signed by Facebook that prohibited the company from sharing user data with third parties without first obtaining user consent.

Zuckerberg was given a deadline of June 18 to respond.

Facebook has responded vigorously to this most recent series of news stories, which began on Sunday night with a story by The New York Times. Facebook said it does not believe it violated the FTC order and views the smartphone manufacturers as service providers. The data sharing was necessary in order for those companies to create mobile Facebook experiences in the pre-app store era, the company said.

Those explanations haven’t quite satisfied some politicians.

This is “another example of questionable business practices by Facebook that could undermine basic consumer privacy,” Nelson said. Facebook began winding down the agreements in April.

Sen. Ed Markey, D-Mass., on Tuesday called on Zuckerberg to return to Congress for more testimony.

Mark Zuckerberg needs to return to Congress and testify why @facebook shared Americans’ private information with questionable Chinese companies. Our privacy and national security cannot be the cost of doing business. https://t.co/nyRbc8xwBY — Ed Markey (@SenMarkey) June 6, 2018

On Wednesday, Howard Dean, the former governor of Vermont, said he was calling it quits on Facebook.

What Facebook did will likely result in imprisonment or other punishment of Chinese young people. Facebook is amoral. It's all about the money for them. My Facebook page is now closed. You can reach me on Twitter. https://t.co/jIafdJw4Ft — Howard Dean (@GovHowardDean) June 6, 2018

“It's all about the money for them,” he wrote. “My Facebook page is now closed. You can reach me on Twitter.”