WASHINGTON (AP) — President Donald Trump is escalating his war on social media companies, preparing to sign an executive order Thursday challenging the liability protections that have served as a bedrock for unfettered speech on the internet.

Still, the move appears to be more about politics than substance, as the president aims to rally supporters after he lashed out at Twitter for applying fact checks to two of his tweets.

The proposed order would direct executive branch agencies including the Federal Communications Commission and the Federal Trade Commission to study whether they can place new rules on the companies — though experts express doubts much can be done without an act of Congress.

Trump and his allies, who rely heavily on Twitter to verbally flog their foes, have long accused the tech giants in liberal-leaning Silicon Valley of targeting conservatives on social media by fact-checking them or removing their posts. The executive order was expected to argue that such actions should cost those companies their protection from lawsuits for what is posted on their platforms.

Companies like Twitter and Facebook are granted liability protection under Section 230 of the Communications Decency Act because they are treated as "platforms," rather than "publishers," which can face lawsuits over content.

A similar executive order was previously considered by the administration but shelved over concerns it couldn't pass legal muster and that it violated conservative principles on deregulation and free speech.

Two administration officials outlined the draft order on the condition of anonymity because it was still being finalized Thursday morning. But a draft was circulating on Twitter — where else?

"This will be a Big Day for Social Media and FAIRNESS!" Trump tweeted.

Press secretary Kayleigh McEnany said the Twitter fact checks reflected "bias in action" and Trump aimed to sign the order by the end of the day.

Trump on Wednesday claimed tech giants "silence conservative voices." "We will strongly regulate, or close them down, before we can ever allow this to happen."

Trump and his campaign reacted after Twitter added a warning phrase to two Trump tweets that called mail-in ballots "fraudulent" and predicted "mail boxes will be robbed." Under the tweets, there's now a link reading "Get the facts about mail-in ballots" that guides users to a page with fact checks and news stories about Trump's unsubstantiated claims.

Trump accused Twitter of interfering in the 2020 presidential election" and declared "as president, I will not allow this to happen." His campaign manager, Brad Parscale, said Twitter's "clear political bias" had led the campaign to pull "all our advertising from Twitter months ago." In fact, Twitter has banned political advertising since last November.

Late Wednesday, Twitter CEO Jack Dorsey tweeted, "We'll continue to point out incorrect or disputed information about elections globally."

Dorsey added: "This does not make us an 'arbiter of truth.' Our intention is to connect the dots of conflicting statements and show the information in dispute so people can judge for themselves."

On the other hand, Facebook CEO Mark Zuckerberg told Fox News his platform has "a different policy, I think, than Twitter on this."

"I just believe strongly that Facebook shouldn't be the arbiter of truth of everything that people say online," he said.

The president's critics, meanwhile, scolded the platforms for allowing him to put forth false or misleading information that could confuse voters.

"Donald Trump's order is plainly illegal," said Oregon Sen. Ron Wyden, a Democrat and advocate for internet freedoms. He is "desperately trying to steal for himself the power of the courts and Congress. ... All for the ability to spread unfiltered lies."

House Speaker Nancy Pelosi said it was "outrageous" that while Twitter had put a fact-check tag on Trump's tweets asserting massive mail-in election fraud, it had not removed his tweets suggesting without evidence that a TV news host had murdered an aide years ago.

"Their business model is to make money at the expense of the truth and the facts that they know," she said of social media giants, also mentioning Facebook. She said their goal is to avoid taxes "and they don't want to be regulated, so they pander to the White House."

Twitter's decision to mark Trump's tweets regarding mail-in balloting came as the president was sparking another social media firestorm, continuing to stoke a debunked conspiracy theory suggesting MSNBC host Joe Scarborough killed a congressional office staffer. Several prominent Republicans have criticized him over those attacks, which haven't been marked with a fact check by the social media company.

The order was also expected to try to hold back federal advertising dollars from Twitter and other social media companies that "violate free speech principles."

Meanwhile, the companies are gearing up to combat misinformation around the November elections. Twitter and Facebook have begun rolling out dozens of new rules to avoid a repeat of the false postings about the candidates and the voting process that marred the 2016 election.

The coronavirus pandemic has further escalated the platforms' response, leading them to take actions against politicians — a move they've long resisted — who make misleading claims about the virus.

Last month, Twitter began a "Get the Facts" label to direct social media users to news articles from trusted outlets next to tweets containing misleading or disputed information about the virus. Company leaders said the new labels could be applied to anyone on Twitter and they were considering using them on other topics.

The Democratic National Committee said Trump's vote-by-mail tweets should have been removed, not just flagged, for violating the company's rules on posting false voting information.

"After taking too long to act, Twitter once again came up short out of fear of upsetting Trump," the party said in a statement.

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AP writers Amanda Seitz and David Klepper contributed.