WASHINGTON — President Trump on Thursday signed an executive order that could open the door for federal regulators to punish Facebook, Google, and Twitter for the way they police content online, issuing a major broadside against Silicon Valley that quickly triggered wide-ranging political opposition and threats of a legal challenge.
Trump has portrayed the order as an attempt to stamp out political bias on the part of the country’s largest social media platforms. His directive comes days after Twitter steered viewers of some of the president’s tweets to news articles that fact-checked his claims, a move Trump said was a form of censorship.
‘‘We’re here today to defend free speech from one of the greatest dangers,’’ Trump said before signing the document.
But advocates for the tech sector, lawmakers in Congress, and a variety of legal experts from across the political spectrum Thursday doubted the legality of Trump’s draft proposal and feared its implications for free speech.
Others questioned whether the US government even could carry out the order as the president intended.
‘‘This is simply setting the wheels of law enforcement and regulation in motion against a private company for questioning the president,’’ said Matt Schruers, president of the Computer and Communications Industry Association, a Washington trade group that represents Facebook, Google, and other major tech companies.
Trump’s order would pave the way for US agencies to revisit and potentially undo longstanding legal protections known as Section 230, which spares tech giants from being held liable for the content they allow online and their own moderation decisions. The directive specifically could open the door for the Federal Communications Commission to rethink the scope of the law, the people familiar with the document said.
A change could have dramatic free-speech implications and wide-ranging consequences for a broad swath of companies reliant on doing business on the Internet.
The order also may channel complaints about political bias to the Federal Trade Commission, which would be encouraged to investigate whether technology companies’ content-moderation policies are in keeping with their pledges of neutrality.
‘‘In a country that has long cherished the freedom of expression, we cannot allow a limited number of online platforms to handpick the speech that Americans may access and convey online,’’ according to an undated draft version of the executive order obtained by the Post late Wednesday.
The order marks the White House’s most significant salvo against Silicon Valley after years of verbal broadsides and regulatory threats from Trump and his top deputies.
It is not clear, however, if the FTC and FCC plan to take the actions sought by the president. The agencies are independent, operating separately of Trump’s Cabinet, leaving enforcement to their discretion.