Senior executives from Facebook Inc., Alphabet Inc.’s Google and Twitter Inc. will testify before the Senate Intelligence Committee on Sept. 5 to discuss their efforts to prevent Russian meddling in November elections.

The panel’s top Democrat, Mark Warner, announced plans for the testimony during a hearing Wednesday about foreign attempts to use social media to influence politics in the U.S., saying he wants to hear the companies’ plans and press them do to more.

Warner didn’t specify who from the companies would testify, but a person familiar with the matter said Facebook Chief Operating Officer Sheryl Sandberg will be one of the executives at the hearing.

Wednesday’s hearing was convened a day after Facebook announced it had uncovered a clandestine campaign to exacerbate U.S. political divisions on its platform. Some of the activity by the pages and profiles, which were removed, matched Russia’s efforts around the 2016 presidential elections, when Russian President Vladimir Putin ordered interference with the election to boost Donald Trump’s candidacy.

“Even today almost two years after the 2016 election, foreign actors continue an aggressive and pervasive influence campaign against the united states of America,” The committee’s chairman, Richard Burr, a North Carolina Republican, said at the hearing. He called on companies to participate in an effort to tackle foreign meddling while balancing national security with the interests of businesses and free speech.

“This requires a thoughtful and informed public policy debate,” he said.

Warner said it’s becoming increasingly clear that the Russians previously caught interfering on social media were “just the incompetent ones who made it easy to get caught” and are just a small fraction of the total Russian meddling effort.

Facebook has promised to protect the U.S. and other countries from the influence of organizations seeking to interfere in fair elections, after failing to disclose the Russia-backed effort until long after the 2016 race was decided. It has been hiring security analysts and coordinating with the governments on thousands of leads.

Tuesday’s disclosure underscores the increasing difficulty of staying ahead of ever-evolving strategies by those trying to take advantage of the platform. Facebook said in a blog post the unknown actors behind the latest campaign “went to much greater lengths to obscure their true identities” than Russia-linked groups had in 2016.

In July, the Intelligence Committee’s strongly backed the finding of U.S. intelligence agencies about Russia’s activity in the face of resistance by Trump to acknowledging the conclusions of his own intelligence community.