WASHINGTON — With Congress scrutinizing Facebook over a huge privacy breach, lawmakers are also facing questions about their financial stakes in the social networking giant. And it turns out that Austin Rep. Michael McCaul owns at least $1 million in Facebook stock, the most of anyone in Congress.

McCaul, one of the richest members of the House or Senate, also reported about $30,000 in capital gains from Facebook holdings in 2016, according to a Roll Call analysis of financial disclosures.

The Republican chairs the House Homeland Security Committee. He does not sit on any of the committees that have requested Facebook CEO Mark Zuckerberg discuss the massive data breach by Cambridge Analytica, the firm that used data taken from Facebook users without their knowledge.

Facebook said Wednesday that up to 87 million people had their data improperly shared by the firm, according to a company blog post. The social media giant had initially estimated 50 million users.

A McCaul spokeswoman did not return requests for comment on Wednesday. McCaul reported the Facebook stock and capital gains through his spouse and child, according to Roll Call.

The House Energy and Commerce committee announced Wednesday that Zuckerberg will appear before the panel on April 11. Lawmakers on the Senate Judiciary and Commerce committees also hope to grill Zuckerberg.

California Sen. Dianne Feinstein told the San Francisco Chronicle on Tuesday the Facebook founder has agreed to testify, but "the question is whether it will be on one committee or two."

Roll Call found that 28 lawmakers in both parties owned shares of Facebook in 2016, according to financial reports filed in August. The next filing deadline is May 15.

Three of them are Democrats who sit on committees probing the company: Reps. Kurt Schrader of Oregon and Joseph Kennedy III of Massachusetts, who sit on the energy and commerce committee, and Rhode Island Sen. Sheldon Whitehouse, a member of the Senate Judiciary Committee.

One other Texas Republican, Midland Rep. Mike Conaway, also made Roll Call's list. Conaway did not report owning any Facebook stock in 2016, but he did report $2,501 in capital gains, meaning that he likely sold shares that year.

He does not serve on any of the committees that have invited Zuckerberg to testify.