The leaders of Twitter, Google, and Facebook have faced strong criticism from US senators over content moderation in a high-profile hearing.
Lawmakers from both the Democrat and Republican parties are assessing the companies' tremendous power to disseminate speech and ideas, less than one week before the US presidential election.
'Powerful arbiters of truth'
In their opening remarks, Mark Zuckerberg, Sundar Pichai, and Jack Dorsey defended section 230 of the "Communications Decency Act", a controversial law which protects platforms from legal proceedings related to content published by third parties.
Facebook CEO Zuckerberg acknowledged that Congress "should update the law to make sure it's working as intended.''
Meanwhile, Twitter co-founder Dorsey urged caution and warned that undermining section 230 would remove much more online content and "impose severe limitations" on platforms' ability to tackle harmful content.
Sundar Pichai also appealed to senators to be "very aware of the consequences" that legal reform might have on businesses and consumers.
Wednesday's Senate hearing was held via videoconference in front of members of the commerce committee of the upper house of US Congress.
Republican Senator Roger Wicker, who chairs the committee, called for a sweeping reform of the law to strengthen the accountability of tech giants.
"My concern is that these platforms have become powerful arbiters of truth and content that users can access," said Senator Wicker.
"The American public is poorly informed about the decision-making process when content is moderated and users have little recourse when it is censored or restricted," he added.
Criticism first focused on Twitter, which has been accused by Republicans of bias in its moderation of content, specifically on posts by US President Donald Trump.
Twitter has repeatedly flagged tweets by President Trump for violating policies by alleging that mail-in ballots would lead to a fraudulent election.
"Your platform allows foreign dictators to publish their propaganda without restriction, while you systematically restrict the president of the United States," Senator Wicker stated.
Jack Dorsey defended his platform's actions to the hearing, saying that the network reacts as quickly as possible to moderate content deemed inappropriate.
Facebook and Twitter were also condemned for taking action on a controversial article by the New York Post about Democrat nominee Joe Biden, and his son Hunter.
Republican senator Ted Cruz, in particular, accused Twitter of "egregious" conduct by limiting the spread of the article.
But Democrat Senator Brian Schatz denounced the hearing as a "sham" and stated that Republicans were "trying to bully the heads of private companies into making a hit job" on political leaders.
The social media giants also faced scrutiny on their efforts to police misinformation ahead of the election, their policies on political advertising, and rules on hate speech.