WASHINGTON — President Trump is preparing to sign an executive order Thursday that could open the door for federal officials to try to penalize Facebook, Google and Twitter for the way they moderate content on their sites, according to two people familiar with the matter, opening a major rift between Washington and Silicon Valley with potentially dramatic free-speech implications.

The wide-ranging order comes two days after Twitter took the rare step of labeling one of the president’s tweets and linking viewers to news articles that fact-checked his claims. The move infuriated Trump and his supporters, who quickly blasted Twitter and its peers in Silicon Valley for engaging in censorship and exhibiting political bias, charges the companies have long denied.

Trump’s directive chiefly seeks to embolden federal regulators to rethink a portion of law known as Section 230, which spares tech companies from being held liable for the comments, videos and other content posted by their users, according to the two sources, who requested anonymity to describe a document that could still evolve and has not been officially signed by the president.

It would task the Commerce Department to petition the Federal Communications Commission to open a rulemaking proceeding to reconsider the scope of the law, the people familiar with the document said. It also would seek to channel complaints about political bias to the Federal Trade Commission for investigation, which would be encouraged to probe if tech companies’ content-moderation policies are in keeping with their pledges for neutrality. Lastly, it would require federal agencies to review their spending on social-media advertising, according to the people familiar with the White House’s thinking.

The executive order has gone through multiple iterations in recent years, and it may still change, the sources cautioned. Even so, it would be up to the FCC and FTC, two independent agencies operating outside the president’s cabinet, to determine exact courses of action once Trump signs it.

Still, it 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 also may raise fresh, thorny questions about the First Amendment, the future of expression online and the extent to which the White House can properly – and legally – influence the decisions that private companies make about their apps, sites and services.

The White House declined to comment. A White House spokesperson told reporters earlier Wednesday that the president would sign an executive order “pertaining to social media” on Thursday, but didn’t provide further details. Trump later in the evening again charged the tech industry sought to “censor” conservatives entering the 2020 election.

The FCC and FTC did not immediately respond to requests for comment. Facebook did not have immediate comment. Twitter and YouTube did not immediately respond to requests for comment.

Trump is one of social media’s most prolific, influential users, armed with a Twitter account that reaches more than 80 million people and a campaign war chest that’s made the president one of the most pervasive advertisers on Facebook and Google. But he is also one of the web’s most controversial voices. He has previously shared and tweeted posts, photos and videos that appear to run afoul of major tech companies’ guidelines that prohibit or discourage harmful, abusive or false content.

For years, Twitter in particular largely allowed Trump to share his views unfettered anyway, believing even his most controversial tweets were in the public interest. But fierce blowback eventually forced Twitter to reconsider its hands-off approach, culminating in the company’s first-ever attempt Tuesday to label the president’s tweets about mail-in ballots.

Trump responded by claiming major social-media companies are biased, threatening to “strongly regulate, or close them down” in response.

Until this week, Trump had issued only threats to regulate or penalize Facebook, Google-owned YouTube and Twitter over a range of claims, even suggesting at one point the industry tried to undermine his election. Previously, though, the White House has backed down, even shelving prior versions of its executive order targeting social-media companies.

In July, the president convened a “social media summit” at the White House featuring GOP lawmakers and Republican strategists, an event seen at the time as a precursor for further action to come. The event drew sharp rebukes from digital experts and congressional Democrats, who felt Trump had used the backdrop of the White House to condone some of his supports’ most provocative, controversial online tactics – the very kind of behavior tech companies often try to combat.

That same month, the Justice Department opened a wide-ranging review of the tech industry, which since has blossomed into a full inquiry on Section 230. Repeatedly, Attorney General William Barr has raised the potential that the U.S. government could seek changes to the rules. “No longer are tech companies the underdog upstarts,” Barr said in a speech this February, reflecting on the origin of the statute. “They have become titans.”

The law itself is controversial. It allows tech companies the freedom to police their platforms for abuse without fear of lawsuit. But critics say those exceptions have also allowed some of Silicon Valley’s most profitable companies to skirt responsibility for the harmful content that flourishes on their platforms online, including hate speech, terrorist propaganda and election-related falsehoods.

Republicans also believe that Facebook, Google and Twitter should be held accountable for perceived political bias, a call echoed by White House officials and Republican lawmakers in Congress alike.