The company has been under intensifying pressure from Congress to be more transparent about political activities conducted on the online network. Stretch is expected to say that an internal Facebook audit discovered that the fake accounts linked to a Russian company produced 80,000 posts between 2015 and 2017.
Those posts appeared on the news feeds of 29 million users but may have reached as many as 126 million people because of user activity on the site.
The finding sheds new light on the scale of Russia’s effort to spread divisive propaganda online during the 2016 presidential race.
In September, Facebook revealed that it had sold more than $100,000 in political ads to the Internet Research Agency, a “troll farm” in St. Petersburg, which produced roughly 3,000 political ads.
Stretch will tell Congress that approximately 11.4 million people saw at least one of those Russian-linked political ads, according to the draft testimony obtained by ABC News.
The ads promoted fake Facebook pages, which produced the 80,000 pieces of content between January 2015 and August 2017.
The 80,000 posts made up roughly 1-in-23,000 pieces of content on the site during that period of time.
“Though the volume of these stories was a tiny fraction of the overall content on Facebook, any amount is too much,” Stretch is expected to tell the Senate panel. “Those accounts and Pages violated Facebook’s policies -- which is why we removed them, as we do with all fake or malicious activity we find.”
While Facebook and Twitter have taken new steps in recent days to self-police and address concerns, some are pushing legislation to increase transparency across the entire industry.
“I think the American people deserve a full accounting both of not only what happened in 2016, but what these platforms are doing to close these vulnerabilities going forward,” Laura Rosenberger, director of the Alliance for Securing Democracy, told ABC News. “This activity didn't stop on November 8th.”
Less is known about the role fake Twitter accounts may have played in the 2016 election. Twitter took the unusual step last week of banning Russian media outlets RT and Sputnik from advertising on the site after finding both had used Twitter ads in an attempt “to interfere with the election on behalf of the Russian government.”
Like Facebook, Rosenberger said Twitter plays an important role in shaping the political conversation in the country. “I mean certainly there's no doubt that the president of the United States believes that Twitter is a very important platform for communication,” she said. “So I think that if he thinks it's an important platform I think certainly the Russians believe it's an important platform.”
Twitter has uncovered a total of 2,752 accounts linked to the Internet Research Agency -- more than 10 times the number of accounts initially disclosed to Congress -- and has identified the accounts for congressional investigators, according to a source familiar with the company's testimony Tuesday.
Advance testimony obtained by ABC News shows Twitter will emphasize the limited amount of Russian activity on the platform.
"It’s important to place those numbers in scale: the 36,746 automated accounts that we identified as Russian-linked and tweeting election-related content represent approximately 1/100th of a percent [0.012%] of the total accounts on Twitter at the time," Twitter's representative is expected to testify Tuesday.
Google, in a blog post Monday evening ahead of this week's hearings, revealed the results of its own internal investigation into Russian use of the platform.
According to the audit, two accounts linked to the Russian troll farm spent $4,700 on ads on Google platforms.
Google also found "evidence that Gmail accounts associated with the campaign were used to open accounts on other platforms" and has shared that information with other platforms.
Tuesday’s hearing is one of three scheduled this week on Russian use of social media. On Wednesday, Facebook, Twitter and Google will also testify before the House and Senate Intelligence Committees.