Facebook, Google and Twitter are going to be questioned by Republican senators on Wednesday over allegations the platforms are biased against conservatives.
Just days ahead of the US election, the chief executives of the three companies will appear remotely before the Senate commerce committee.
President Donald Trump has ordered a review of legal protections for social media platforms after Twitter fact-checked two of his tweets which falsely claimed postal votes were fraudulent - and hid another which it said glorified violence.
Ahead of the hearing, senators on the commerce committee are expected to examine proposals to reform the ways that social media companies moderate content.
The platforms are currently protected by a law passed in 1996 which means that, in most circumstances, they are not liable for the content of their users' posts because they are a neutral platform rather than a publisher.
However, Section 230 of the Communications Decency Act allows them to perform "good faith" content moderation - as a publisher would - without assuming the liability that publishers have.
Some instances of this "good faith" moderation have been seen as politically motivated by conservatives, in particular their unprecedented decision to censor a story that could have influenced voters ahead of the election.
Earlier this month, Facebook and Twitter blocked users from sharing an unverified story about Hunter Biden - the son of the Democratic presidential candidate Joe Biden - amid concerns from experts in foreign interference that the story was highly suspicious.
Twitter's chief executive Jack Dorsey later apologised for preventing users from posting links to the story without an explanation, although he stood by the move to block the links themselves following allegations that the company had failed to address foreign interference in the 2016 election.
Mr Trump criticised the blocks without addressing concerns about the integrity of the journalism itself, saying: "So terrible that Facebook and Twitter took down the story of 'Smoking Gun' emails related to Sleepy Joe Biden and his son, Hunter, in the New York Post."
Mr Trump, who has persistently accused both traditional and social media of being biased against him, had previously complained that social media platforms "totally silence conservative voices".
Earlier this year he promised to "close them down before we can ever allow this to happen", and subsequently signed an executive order calling on federal agencies to review Section 230.
The Department of Justice, led by Attorney General William Barr, has unveiled proposals for reform following that review - recommending giving a proper definition to "good faith" that would "encourage platforms to be more transparent and accountable to their users".
Further changes would tackle platforms' immunity when moderating content that is "otherwise objectionable", a vague term in the statute which the department said gives the platforms the ability to remove content "arbitrarily".
In his opening statement for Wednesday's hearing, Mark Zuckerberg said Congress "should update the law to make sure it's working as intended", adding: "We don't think tech companies should be making so many decisions about these important issues alone."
Twitter's Jack Dorsey and Google's Sundar Pichai urged caution.
"Undermining Section 230 will result in far more removal of online speech and impose severe limitations on our collective ability to address harmful content and protect people online," Mr Dorsey said.
Mr Pichai said that the lawmakers needed "to be very thoughtful about any changes to Section 230 and to be very aware of the consequences those changes might have on businesses and consumers".