Representatives for Facebook, Google, and Twitter will appear in front of congress on November 1st to provide testimony on Russian election interference.

Facebook’s Colin Stretch, Twitter’s Sean Edgett and Google’s Kent Walker will represent their companies, the technology giants said. All three tech companies found evidence of ad tampering over the course of internal investigations this year, and subsequently reported those findings to congress.

The lawyers will testify before the Senate and House intelligence committees — two of the congressional panels searching for evidence that Russia sought to interfere in the U.S. election or potentially colluded with the Donald Trump campaign.

Trump has repeatedly denied any collusion with the Russians, and to date, no evidence has emerged to suggest there was collusion. U.S. officials also have said Russia’s alleged meddling didn’t go so far as to change any votes in the election.

Facebook revealed last month that a group with alleged ties to the Russian government ran $100,000 worth of ads on the platform promoting “divisive” causes like Black Lives Matter. U.S. media reports also indicate Russians purchased similar ads on Google.

In releasing the ads to Congress, Sandberg said, “It’s important that [the investigators] get the whole picture and explain that to the American people.” In response to the Russian ad buys, Sandberg said Facebook is hiring 4,000 new employees to oversee ads and content. She said the company also is using “machine learning and automation” to target fake accounts that spread fake news.

Google, for its part, found thousands of dollars in ads were purchased by Russian agents, and continues to investigate over $50,000 in questionable ad purchases from accounts that haven’t been confirmed to be bad actors yet.

In addition, Twitter has taken action against suspected Russian troll accounts, suspending 22 accounts that corresponded with fake accounts used on Facebook.