Facebook and Twitter executives are expected to defend their companies in congressional hearings - arguing they are adamant to find foreign actors who want to do the US harm weeks before midterm elections.
Twitter chief executive Jack Dorsey will face angry Republicans who claim the companies have shown evidence of bias against conservatives.
In prepared evidence released ahead of a House of Representatives hearing on Wednesday, Mr Dorsey said his company does not use political ideology to make decisions.
Missing from the grilling conversations will be Google, which refused to make senior executives available for the Senate intelligence hearing.
Congress has sharply criticised social media companies over the last year as it has become clear they were at the forefront of Russia’s interference in the 2016 elections and beyond.
The scrutiny has led to additional backlash over the companies’ respect for user privacy and whether conservatives are being censored - frustrations that are particularly heightened ahead of the midterms.
"The companies have made progress, the government has made progress, but the bad guys have made progress as well," said Virginia senator Mark Warner, the senior Democrat on the Senate intelligence committee - which will hear from Facebook and Twitter on the subject of foreign interference.
Mr Warner has proposed a series of ways the companies could be regulated for the first time but in the afternoon hearing Mr Dorsey will focus on bias and the platform's algorithms.
President Donald Trump and other Republicans have pushed the idea ahead of the elections - Twitter is "shadow banning" some in the party because of the ways search results have appeared, but Twitter denies this claim.
The panel invited Larry Page, chief executive of Google’s parent company Alphabet, but the company said it would send a lower-ranking executive.
The committee rejected that offer, and is expected to have an empty chair at the hearing for Mr Page.
Senate intelligence committee chairman Richard Burr said Google does not "understand the problem" if it does not want to work with the government.
The back-and-forth with Google is the latest in a year’s worth of attempts by Congress to force the companies to focus more sharply on the Russian interference issue.
While Mr Burr says he believes Facebook and Twitter understand the problem, it took both companies several months last year to acknowledge they had been manipulated.
In prepared remarks for the hearing, Facebook’s number two executive Sheryl Sandberg details many ways the company is addressing the problem but reiterates the company was slow to spot it.
Special counsel Robert Mueller charged 13 Russians earlier this year on an elaborate plot to disrupt the 2016 US presidential election by creating fake accounts which pushed divisive issues on social media.
In her evidence, Ms Sandberg details continuing efforts to take down material linked to the Russian agency, including the removal this year of 270 Facebook pages.
But she says the company’s overall understanding of the Russian activity in 2016 is limited “because we do not have access to the information or investigative tools” that the US government has.