US President Donald Trump has signed an executive order aimed at removing some of the legal protections given to social media platforms.
He said the firms had "unchecked power" to censure and edit the views of users.
President Trump has regularly accused platforms such as Twitter and Facebook of stifling conservative voices.
The order, which is expected to face legal challenges, comes after Twitter decided to append fact-check labels to two of his tweets this week.
On Wednesday Trump accused the company of election interference after it added a warning label to the tweets about claims of widespread fraud in mail-in voting - also known as postal votes.
Twitter and other social media platforms strongly condemned the executive order.
And early on Friday, Twitter hid one of President Trump's tweets from his profile, saying it violates rules about glorifying violence.
What does the executive order say?
The order sets out to clarify the 1996 Communications Decency Act, which offers online platforms such as Facebook, Twitter and YouTube legal protection in certain situations.
Under Section 230 of the law, social networks are not generally held responsible for content posted by their users.
The executive order points out that this immunity does not apply if a social network edits content posted by its users, and calls for legislation from Congress to "remove or change" section 230.
It also says "deceptive" blocking of posts, including removing a post for reasons other than those described in a website's terms of service, should not be offered immunity.
Republican Senator Marco Rubio is among those arguing that the platforms take on the role of a "publisher" when they add fact-check labels to specific posts.
"The law still protects social media companies like Twitter because they are considered forums not publishers," Mr Rubio said.
"But if they have now decided to exercise an editorial role like a publisher, then they should no longer be shielded from liability."
The executive order also calls for:
- the Federal Communications Commission (FCC) to spell out what type of content blocking will be considered deceptive, pretextual or inconsistent with a service provider's terms and conditions
- a review of government advertising on social-media sites and whether those platforms impose viewpoint-based restrictions
- the re-establishment of the White House "tech bias reporting tool" that lets citizens report unfair treatment by social networks
Meanwhile, Twitter has hidden one of President Donald Trump's tweets from his profile, saying it violates rules about glorifying violence.
But instead of being deleted, it has been replaced with a warning and can be viewed by clicking on it.
The warning says "Twitter has determined that it may be in the public's interest for the Tweet to remain accessible."
It is the latest in an escalating row between Twitter and the White House.
Trump was tweeting about the US city of Minneapolis, which has seen consecutive nights of protests following the death of a black man in police custody.
The president said he would "send in the National Guard", and followed that up with a warning that "when the looting starts, the shooting starts."
That second tweet was hidden by Twitter for "glorifying violence".
Twitter's policy of adding a warning to, rather than deleting, tweets that break its rules when it comes to major public figures was announced in mid-2019. But the social network has never used it on Mr Trump - nor deleted any of his tweets before.