Facebook, Google and Twitter plan to tell congressional investigators this week that the scope of Russia’s campaign to spread disinformation on their sites — and to potentially disrupt the 2016 U.S. presidential race — is much broader than the companies initially reported.

At Facebook, roughly 126 million users in the United States may have seen posts, stories or other content created by Russian government-backed trolls around Election Day, according to a source familiar with the company’s forthcoming testimony to Congress. Previously, Facebook had only shared information on ads purchased by Kremlin-tied accounts, revealing that they reached more than 10 million U.S. users.

Google, which previously had not commented on its internal investigation, will break its silence: In an early blog post, the search giant confirmed that it discovered about $4,700 worth of search-and-display ads with dubious Russian ties. It also reported 18 YouTube channels associated with the Kremlin’s disinformation efforts, as well as a number of Gmail addresses that “were used to open accounts on other platforms.”

Twitter, lastly, is under pressure to provide more details to federal lawmakers. In September, it faced criticism from Sen. Mark Warner and other top investigators for failing to perform a exhaustive probe of disinformation spread by known Russian trolls, known as the Internet Research Agency.