Senators angry with social media companies.

WASHINGTON — Facebook CEO Mark Zuckerberg and other social media executives came under pressure from both sides of the political aisle Monday to testify in the U.S. Senate on how a political consulting firm gained access to the data of millions of Facebook users during the 2016 presidential campaign.

Sens. John Kennedy, R-La., and Amy Klobuchar, D-Minn., wrote to the chairman of the Senate Judiciary Committee demanding that top executives from Facebook, Twitter and Google be brought in for questioning about their efforts to police their own platforms for abuse and interference in U.S. elections.

The senators’ demand followed the revelation over the weekend that Cambridge Analytica, a political consulting firm used by President Trump’s 2016 campaign, had employed quizzes and other methods to obtain personal information from 50 million Facebook users without permission. The company has touted its use of psychological profiling as a way to predict voter behavior.

“Facebook, Google and Twitter have amassed unprecedented amounts of personal data and use this data when selling advertising, including political advertisements,” the senators wrote. “The lack of oversight on how data is stored and how political advertisements are sold raises concerns about the integrity of American elections as well as privacy rights.”

In a statement Monday, Facebook said it has “hired a digital forensics firm, Stroz Friedberg, to conduct a comprehensive audit of Cambridge Analytica,” and that Cambridge Analytica has agreed to comply. “We remain committed to vigorously enforcing our policies to protect people’s information,” Facebook’s statement said.

The three large Bay Area technology companies have lost some of their luster in Washington amid revelations that the Russian government used their platforms to interfere in the last presidential election, and warnings that misuse in future elections is likely.

Last fall, Kennedy and other senators sharply questioned executives from the three giant social media platforms after the companies revealed that the Russian disinformation campaign had reached many more users than they initially disclosed. Both of California’s senators sit on the Judiciary Committee. Sen. Dianne Feinstein is its top-ranking Democrat, and Sen. Kamala Harris is the committee’s newest member. Neither joined the Kennedy-Klobuchar letter.

Feinstein and Harris also sit on the Senate Intelligence Committee, which scheduled an open hearing Wednesday on threats to elections and voting systems, with testimony planned from administration officials and state organizations representing election officials.

In the House, Rep. Adam Schiff, D-Burbank, the Intelligence Committee’s top Democrat, reiterated his call for testimony from officials of Cambridge Analytica and Facebook, saying the Menlo Park social media company “must explain the long delay” in suspending its relationship with the consulting firm and “how they will ensure the protection of users from malicious access to their personal information.”