Facebook chief Mark Zuckerberg and Twitter CEO Jack Dorsey testified remotely to the session, called to discuss "censorship and suppression of news articles" and the "handling of the 2020 election" by the platforms.
The senators are deeply divided by party over the integrity and results of the election itself. At one point, the social network applied warning labels to more than a third of Trump's tweets after polls closed.
Prominent Republican senators - including the Judiciary Committee chairman, Lindsey Graham of SC - have refused to knock down Trump's unfounded claims of voting irregularities and fraud, as misinformation disputing President-elect Joe Biden's victory has flourished online.
Zuckerberg and Dorsey promised lawmakers last month that they would aggressively guard their platforms from being manipulated by foreign governments or used to incite violence around the election results. Over last weekend, Twitter affixed a fact check label to more than 30 of his election-related tweets and retweets between Friday and Monday morning.
In response to proposals concerning Section 230, a federal law that grants websites legal immunity for curating the content on their platforms, Dorsey will warn that a repeal could lead to increased content removals and frivolous litigation while making it harder to address truly harmful material online.
Facebook also moved two days after the election to ban a large group called "Stop the Steal" that Trump supporters were using to organize protests against the vote count.
The 350,000-member group echoed Mr Trump's baseless allegations of a rigged election rendering the results invalid.
As of Monday, Facebook appeared to have made them harder to find, though it was still possible to locate them, including some groups with thousands of members.
Warily eyeing how the companies wield their power to filter speech and ideas, Trump and the Republicans accuse the social media platforms of anti-conservative bias.
Supporters of President Donald Trump
Democrats also criticise them, though for different reasons. Biden has heartily endorsed such an action.
Facebook and Twitter defended their handling of U.S. election misinformation at a heated congressional hearing Tuesday where one key senator assailed the platforms for being the "ultimate editor" of political news.
The CEOs, Jack Dorsey of Twitter and Mark Zuckerberg of Facebook, defended their content moderation practices at a congressional hearing scheduled after the platforms chose to block stories from the New York Post that made claims about the son of then-Democratic presidential candidate Joe Biden.
Zuckerberg and Dorsey, along with Alphabet-owned Google's Sundar Pichai, also appeared before the Senate Commerce Committee in October for a hearing in which Republican lawmakers questioned the companies about their content moderation decisions.
"When you have companies that have far more power than traditional media outlets, something has to give", he said.
This autumn, Facebook said it removed a small network of accounts and pages linked to Russia's Internet Research Agency, the "troll factory" that has used social media accounts to sow political discord in the U.S. since the 2016 election.
Dorsey was preemptively addressing questions sure to arise over Twitter flagging dozens of President Donald Trump's tweets related to the election - especially those questioning the results.
Democrats focused on the spread of misinformation by Trump, a Republican, and his supporters. They criticize the tech CEOs for failing to police content, blaming the platforms for playing a role in hate crimes and the rise of white nationalism in the U.S. And that criticism has extended to their efforts to stamp out false information related to the election.