The Supreme Court on Thursday blocked a Texas law that would ban social media companies from removing users and the content they post because of a particular viewpoint expressed.
The court did not elaborate on the decision, which is temporary while legal challenges proceed through lower courts.
"We are relieved that the First Amendment, open internet, and the users who rely on it remain protected from Texas's unconstitutional overreach," said Chris Marchese, an attorney for NetChoice, the industry trade group representing Meta, TikTok, YouTube and others, in a statement.
NetChoice says the law, which took effect earlier this month, would effectively force social media platforms to disseminate dangerous content, including propaganda, hate speech and threats of violence, in violation of their First Amendment rights.
Republican sponsors of the law -- the first of its kind in the country -- say the measure is meant to end alleged censorship of conservative users on the social networks, which they argue are modern-day "public squares."
Four justices -- Elena Kagan, Samuel Alito, Clarence Thomas and Neil Gorsuch -- indicated they would have let the Texas law remain in force while the legal battle plays out.
Justice Alito, in a dissent joined by Thomas and Gorsuch, explained that he would not have interfered with a lower court decision to let the law take effect, suggesting that the justices would likely hear the dispute on appeal in due time.
"The law before us is novel, as are applicants' business models," wrote Alito "It is not at all obvious how our existing precedents, which predate the age of the internet, should apply to large social media companies."
At the heart of the dispute is the First Amendment's protection of freedom of speech and thorny questions around private companies' censorship across networks of more than 50 million users.
Texas Republicans enacted the law in response to longstanding frustration from conservatives who feel silenced or sidelined by the media companies' moderation policies.
Texas Attorney General Ken Paxton, who is leading defense of the law, has argued the companies' size rivals public utilities in influence and importance to Americans' daily lives and therefore should be regulated accordingly.
"The platforms are the 21st-century descendants of telegraph and telephone companies: that is, traditional common carriers," he wrote. The government can require common carriers to generally accept all users.
The NAACP and Anti-Defamation League are siding with the companies, warning of enhanced risk to public safety if the law is allowed to stand and more like it take hold across the country. They say the private companies have a right and obligation to police content on their sites to ensure the welfare of members.
Florida's GOP-controlled state legislature enacted a similar law this spring, but it was temporarily blocked by a federal appeals court last week.
"Social media platforms exercise editorial judgment that is inherently expressive," wrote Judge Kevin Newsom in the panel's decision. "When platforms choose to remove users or posts, deprioritize content in viewers' feeds or search results, or sanction breaches of their community standards, they engage in First Amendment-protected activity."
If and when the Supreme Court takes up the Florida or Texas law on the merits, the decision could have sweeping impact on the future of speech on the Internet and private companies' ability to moderate content on their sites, online legal experts say.