The creator of the world’s biggest online social network will appear before Congress this afternoon to answer questions about a recent, massive data scandal.

Iowa Senator Chuck Grassley will be questioning Facebook founder and CEO Mark Zuckerberg about how and why the political data firm Cambridge Analytica gained access to personal data from 87-million Facebook users.

Grassley says, “This case clearly broke consumer trust and has been a catalyst for an overdue conversation about data privacy.” Facebook has more than two-billion users globally. Grassley says he can’t be forthcoming about how he’ll question Zuckerberg as it will depend on the testimony he gives before the joint hearing of the Senate Judiciary and Commerce committees.

Grassley, who chairs the Judiciary Committee, says some senators are already introducing legislation to more tightly regulate Facebook and other social media outlets. “I’m not going to say whether we need more legislation until after we get this hearing over and we study the issue a little bit,” Grassley says. “Mr. Zuckerberg has said that maybe legislation is needed, in fact, I think he’s even encouraged some legislation and regulation.”

If Zuckerberg is apologetic and makes it clear Facebook is doing all it can to keep users’ personal information safe, Grassley says it will set the tone. “We have to have strong testimony that they’ve learned a lesson and that they’re going to be transparent with people on what the privacy rights are, how that data is used, what people can do if they don’t want it used, and that it’s pretty simple,” Grassley says. “Short of that, I think they’re going to be inviting legislation.” Anyone who’s signed up for a social media platform has likely seen, Grassley says, how privacy policies are often buried behind layers of settings or they’re shrouded in confusing legal language.

“Consumers need a better understanding of these companies’ practices to make better informed decisions about their personal information,” Grassley says, “and that means renewed transparency from companies that harvest our information.”

Zuckerberg is scheduled to testify starting around 1:30 p.m. central time.