Facebook is in the political hot seat yet again after revelations that personal info on millions of users ended up in the hands of a data-analytics firm used by Donald Trump’s 2016 election campaign — without the knowledge or permission of those users.

In the wake of the Facebook incident, two U.S. Senators — Sens. Amy Klobuchar (D-Minn.) and John Kennedy (R-La.) — called for hearings to grill Facebook CEO Mark Zuckerberg and the chief execs of Google and Twitter about how the companies share personal user data.

Facebook shares fell more than 6% Monday after reports about the user data improperly being obtained by Cambridge Analytica, a consulting firm used by Trump’s presidential campaign. On Friday, the social giant announced that it kicked Cambridge Analytica and its parent company off the platform, claiming the researcher who provided the data to them violated Facebook’s policies.

In a letter Monday, the two senators asked Senate Judiciary Committee chairman Chuck Grassley (R-Iowa) to hold hearings on the subject and raised the specter of introducing new legislation to address handling of personal data.

“While Facebook has pledged to enforce its policies to protect people’s information, questions remain as to whether those policies are sufficient and whether Congress should take action to protect people’s private information,” Klobuchar and Kennedy wrote in the letter.

Facebook claimed that Cambridge Analytica did not use the data on the more than 50 million users as part of its work for the 2016 Trump campaign. Facebook has previously been hauled in front of Congress — along with other tech companies — over their role in spreading misinformation planted by orgs with ties to the Russian government designed to influence the 2016 U.S. presidential election.

Social-media platforms have user bases larger than all of the major TV broadcasting companies combined, the senators noted. Today, “Facebook, Google, and Twitter have amassed unprecedented amounts of personal data and use this data when selling advertising, including political advertisements,” Klobuchar and Kennedy 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.”

A hearing before the Senate Judiciary Committee would let lawmakers gather the facts and “assess what measures should be taken before the next elections,” the senators wrote.

Also Monday, European Union officials said they will investigate Facebook’s processes for handling personal user data.

Facebook did not respond to a request for comment on the senators’ call for hearings.