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.