Facebook, Twitter, and Google are facing questions from the US Senate over a key legal protection given to their firms.
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.
At present, the firms cannot be sued over what their users post online, or the decisions they make over what to leave up and take down.The law was passed in 1996.
But some politicians have raised concerns that this "sweeping immunity" encourages bad behaviour.
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 three CEOs will say they need the law to be able to moderate content.However, Facebook's Mark Zuckerberg will add that he supports changes to the rule "to make sure it's working".
According to Sky, Google boss Sundar 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".
Section 230 is the main legal protection for social networks so they don't get sued.
The Act allows them to perform "good faith" content moderation - as a publisher would - without assuming the liability that publishers have.
Originally seen as a way to protect internet providers (like BT or Comcast), it's become the main shield for huge sites like Facebook, Twitter and YouTube, which can't possibly review every post from their users before they go up.
Twitter boss Mr Dorsey has written to the committee to tell them that "weakening Section 230 protections will remove critical speech from the internet". He also argues that the law has allowed smaller companies - such as Twitter once was - to compete with established giants without worrying about vast compliance issues.
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.
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."
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 its users".
Further changes would tackle platforms' immunity when moderating content that is "otherwise objectionable". The department said the vague statute gives the platforms the ability to remove content "arbitrarily".