A Texas law forbidding social media giants from regulating certain forms of online speech has been blocked by the US Supreme Court.
The legislation would have prevented larger tech companies from banning or censoring Texas users for their views.
Republicans in the state said it was necessary to combat what they claimed was social media’s liberal bias.
But tech groups argued that the law was a violation of the private companies’ freedom of speech rights.
In a rare 5-4 ruling, the US’s top court agreed on Tuesday to a request supported by tech giants to temporarily block the law from coming into force.
Industry groups suing against the legislation argued that it violated the right to free speech, which included the freedom of private companies to decide what content to publish on their platforms.
Without the ability to moderate their platforms, Silicon Valley campaigners claimed that the state legislation would have turned Facebook, Twitter and YouTube into “havens of the vilest expression imaginable”.
Texas Governor Greg Abbott, who signed the bill into law in September last year, said at the time that the opposite was true – that the measure was intended to prevent bias against conservative viewpoints and protect free speech.
Social media companies are “our modern-day public square” where debate should flow freely, he argued. “There is a dangerous movement by social media companies to silence conservative viewpoints and ideas”.
The law stated that social media platforms with more than 50 million users could not ban people based on their political viewpoints.
Facebook, Twitter and Google’s YouTube all fell within its scope.
On Tuesday, an unlikely group of five Supreme Court justices – appointed by both Democratic and Republican presidents – joined forces to block the law from taking effect while lawsuits over its legality continue.
The majority, who provided no explanation for the emergency decision, included Justices John Roberts, Brett Kavanaugh, Amy Coney Barrett, Sonia Sotomayor and Stephen Breyer.
Their order follows a separate ruling by another federal court last week which found a similar law in Florida likely violated the right to free speech enshrined in the US Constitution.
In the past few months, a number of Republican-led US states have accused social media companies of being biased against conservative views and have passed laws attempting to constrain them.
The question of how far free speech extends on social media platforms – and whether attempts by US states to legislate against the companies may themselves count as censorship – is likely to be tested increasingly in US courts in the coming years.