Sen. Amy Klobuchar, D-Minn., a member of the Senate Judiciary Committee, went so far as to press for Mark Zuckerberg, Facebook’s chief executive, to appear before the panel to explain what the social network knew about the misuse of its data “to target political advertising and manipulate voters.”

The calls for greater scrutiny followed reports Saturday in The New York Times and The Observer of London that Cambridge Analytica, a political data firm founded by Steve Bannon and Robert Mercer, the wealthy Republican donor, had used the Facebook data to develop methods that it claimed could identify the personalities of individual U.S. voters and influence their behavior. The firm’s so-called psychographic modeling underpinned its work for the Trump campaign in 2016, though many have questioned the effectiveness of its techniques.

But Facebook did not inform users whose data had been harvested. The lack of disclosure could violate laws in Britain and in many U.S. states.

Damian Collins, a Conservative lawmaker in Britain who is leading a parliamentary inquiry into fake news and Russian meddling in the country’s referendum to leave the European Union, said this weekend that he, too, would call on Zuckerberg or another top executive to testify. The social network sent executives who handle policy matters to answer questions in February.

“It is not acceptable that they have previously sent witnesses who seek to avoid answering difficult questions by claiming not to know the answers,” Collins said in a statement.

Over the weekend, Facebook was on the defensive. Top executives took to Twitter to argue that the company’s protections had not been breached, and that Facebook was thus not at fault.

“This was unequivocally not a data breach,” tweeted Andrew Bosworth, a Facebook executive. “No systems were infiltrated, no passwords or information were stolen or hacked.”

This article originally appeared in The New York Times.

MATTHEW ROSENBERG and SHEERA FRENKEL © 2018 The New York Times