The committee’s chairman, a Republican, opened the hearing by attacking the power that social media companies have to moderate content on their platforms, accusing them of making politically slanted calls while hiding behind a decades-old liability shield.
“I don’t want the government to take over the job of telling America what tweets are legitimate and what are not,” said the chairman, Senator Lindsey Graham of South Carolina. “But when you have companies that have the power of government, have far more power than traditional media outlets, something has to give.”
Mr. Graham’s early comments most likely presage a bruising set of questions from the committee’s Republican members.
President Trump and his allies have spent years attacking the Silicon Valley platforms for what they say is bias against conservatives, pointing to the liberal politics of the companies’ employees and instances of moderation that affected Republicans or conservative media. Their evidence for these claims has always been anecdotal, and many right-wing personalities have built big followings online.
Mr. Graham took exception to the way Twitter and Facebook had initially limited the reach of a New York Post article about Hunter Biden, the son of President-elect Joseph R. Biden Jr. The article prompted the committee to demand that the chief executives of the two companies testify.
“That, to me, seems like you’re the ultimate editor,” he said.
Mr. Graham’s comments are reflected in how conservatives are increasingly attacking the companies for the way they’ve handled a fractious period after the presidential election, when President Trump has refused to concede despite Mr. Biden’s insurmountable lead.
Mr. Graham questioned Twitter’s decision to label a tweet from a Republican politician as making a “disputed” claim about election fraud. And he said that the companies were “literally engaged in telling us what’s reliable and what’s not based on cable news commentary or tweets from politicians or average citizens.”
Mark Zuckerberg, the chief executive of Facebook, and Jack Dorsey, Twitter’s chief, are appearing before members of the Senate Judiciary Committee to defend actions by their companies to moderate speech. It is the second time in two months that the two C.E.O.s are testifying but this will probably have more fireworks than their last appearance as their companies took a central role during the recent election.
They will probably face many questions about how their social networks handled vote-related posts, videos and photos. Both companies increased their labeling of election misinformation, including posts by President Trump, while false and misleading content surged.
The committee chairman, Lindsey Graham of South Carolina, called the hearing in October after Twitter and Facebook labeled or limited the reach of a New York Post article about Hunter Biden, the son of President-elect Joseph R. Biden Jr., because of information that was leaked and misleading.
The executives, who have each appeared before Congress several times in recent years about data privacy, disinformation in the 2016 election and content moderation, will face new questions, including whether a continued ban on political ads could jeopardize the Senate runoffs in Georgia and why hateful content is still allowed on their sites.
President Trump and his Republican allies have balked at actions by Twitter and Facebook to repeatedly label and hide the president’s posts for violations of policies against spreading false and misleading information about the election. Twitter was particularly active in labeling Mr. Trump’s tweets on the day of the election and days after.
Democrats, meanwhile, say Facebook and Twitter have been too lax on disinformation and hate speech, allowing figures like Steve Bannon, who recently called for Dr. Anthony Fauci’s beheading, to maintain his Facebook account. They also will point to a rise in anti-Muslim content on Facebook and a rise in hate content across social media.
Of all the social media platforms, Twitter has lately been especially aggressive in disputing inaccurate election-related posts and hiding messages. That means Jack Dorsey, Twitter’s chief executive, may face particular fire while testifying in front of the Senate Judiciary Committee on Tuesday about social media and censorship.
President Trump and other Republican leaders have claimed for months — and increasingly vocally in recent days — that Mr. Dorsey has unfairly cracked down on them. They have threatened to roll back legal protections for Twitter and other social media platforms.
They are likely train their ire on two recent developments. One was Twitter’s decision last month to restrict users from sharing an unsubstantiated New York Post article about Joseph R. Biden Jr.’s son Hunter. Twitter limited the sharing of the article more than Facebook did, drawing cries of censorship from Republicans.
The other focus is likely to be Twitter’s handling of election-related content and, in particular, how the company has appeared to tightly moderate Mr. Trump and other conservatives. Between Election Day and Nov. 5, Twitter labeled 38 percent of Mr. Trump’s 29 tweets and retweets as disputed or misleading, according to a New York Times tally. Some of the tweets were hidden from view.
Last week, Twitter said it had labeled 300,000 tweets related to the presidential election as disputed, or 0.2 percent of the total on the subject. It also said the number of people quote-tweeting messages had dropped 29 percent in the wake of its efforts to discourage the sharing of misinformation.
“We want to be very clear that we do not see our job in this space as done,” Mr. Dorsey said in prepared testimony for the hearing. “Our work here continues, and our teams are learning and improving how we address these challenges and earn the trust of the people who use Twitter. I look forward to continuing to work with you on solutions and building the guideposts for the future internet.”
This will be Mr. Dorsey’s fourth appearance in front of lawmakers in recent years. Last month, he testified before the Senate Committee on Commerce, Science and Transportation along with Google’s chief executive, Sundar Pichai, and Facebook’s chief executive, Mark Zuckerberg.
Mr. Dorsey was asked the most questions at that hearing, with Senator Ted Cruz of Texas and other Republican leaders grilling him over his decision to limit sharing of the New York Post article. Twitter later reversed its decision, allowing people to post links to the article.
On Tuesday, Twitter also introduced Fleets, a feature that allows users to tweet ephemeral messages. People can post photos or text to their Twitter pages temporarily, with the post automatically deleting itself 24 hours later.
Don’t be surprised if Mark Zuckerberg, Facebook’s chief executive, starts to sound repetitive at Tuesday’s Senate Judiciary Committee hearing on censorship and social media. He has done this before.
Five times, in fact. This will be Mr. Zuckerberg’s sixth appearance in front of Congress, and the 36-year-old is now well accustomed to making a pitch about how his social network — the world’s largest — is a force for good. Forget that Facebook is a veritable superspreader of disinformation and confusion across the internet.
Facebook said Mr. Zuckerberg planned to remind lawmakers at the hearing that his platform gives everyone on earth a voice. That included the election this month. In the run-up to Nov. 3, Facebook created the Voting Information Center, a hub of voting data and directions, and directed millions of users to register to vote, among other moves.
As he did in his last virtual visit to Capitol Hill last month, Mr. Zuckerberg is also likely to say some of the laws governing platforms like his own need updating and revisiting. They include Section 230 of the Communications Decency Act, which shields companies like Facebook from liability for the speech hosted on their platforms.
Mr. Zuckerberg is also likely to call again for new regulations on privacy, elections and data portability, Facebook said. He previously asked for guidance in those areas from the federal government.
Lawmakers are likely to focus their questions — again — on whether Facebook censors some of their views. Republican lawmakers in particular have asserted that the company has an anti-conservative bias.
Yet whatever drubbing Mr. Zuckerberg takes, it will probably be less severe than the one Jack Dorsey, Twitter’s chief executive, is given when he, too appears before the committee on Tuesday. That’s because Mr. Zuckerberg has managed to make his social network seem less intrusive than Twitter at blocking and labeling content.
Last month, for instance, Twitter prohibited the sharing of a New York Post article that made unsubstantiated corruption claims about Hunter Biden, the son of President-elect Joseph R. Biden Jr. Facebook did not go as far and made the link to the article less visible in the feeds of users while the article was fact-checked by third-party experts.
Even so, Facebook has cracked down on election-related falsehoods with vigor during and after the election. It shut down Facebook Groups that promoted the “Stop the Steal” movement, which is built around the false idea that the election was stolen from President Trump. Facebook also added more “friction” to slow the flow of misinformation on its network by creating more steps for reading and sharing posts.
The moves have incited a backlash from conservatives, with millions of people threatening to leave Facebook for apps such as Parler, MeWe and Rumble. Those apps have marketed themselves to conservatives and positioned themselves as free-speech sites. They have seen record numbers of new users over the past week, according to Sensor Tower, an app analytics firm.