President Donald Trump's favorite social media platform, Twitter, on Tuesday began fact-checking his posts, applying warning labels to two of his tweets that made misleading claims about mail-in voting.
Twitter's move marked the first time that the social media giant has fact-checked the president within its own platform.
"Get the facts about mail-in ballots," the tags read below two of Trump's tweets.
Trump on Tuesday night accused Twitter of interfering in the 2020 election by "saying my statement on Mail-In Ballots, which will lead to massive corruption and fraud, is incorrect."
"Twitter is completely stifling FREE SPEECH, and I, as President, will not allow it to happen!," he added in another tweet.
When clicked, the links lead users to a page that in part reads: "Trump falsely claimed that mail-in ballots would lead to 'a Rigged Election.' However, fact-checkers say there is no evidence that mail-in ballots are linked to voter fraud."
A Twitter spokesperson told CNBC that the tweets "contain potentially misleading information about voting processes and have been labeled to provide additional context around mail-in ballots."
The decision follows Twitter's move last month to change its approach, the spokesperson added.
The White House did not immediately respond to a request for comment from CNBC.
Later Tuesday evening, Trump campaign manager Brad Parscale accused Twitter of trying to block the president from reaching voters.
"We always knew that Silicon Valley would pull out all the stops to obstruct and interfere with President Trump getting his message through to voters," Parscale said in a statement.
"Partnering with the biased fake news media 'fact checkers' is only a smoke screen Twitter is using to try to lend their obvious political tactics some false credibility," Parscale said. "There are many reasons the Trump campaign pulled all our advertising from Twitter months ago, and their clear political bias is one of them."
In fact, Twitter last October banned all political ads from the platform, a move that Parscale complained about at the time.
Calls for Twitter to intervene in the president's account grew earlier Tuesday, after Trump continued making baseless suggestions that MSNBC anchor Joe Scarborough might have been involved in the death in 2001 of his former intern when he served in Congress.
The staffer's widower wrote to Twitter CEO Jack Dorsey, asking him to remove Trump's tweets on the matter. "I'm asking you to intervene in this instance because the President of the United States has taken something that does not belong to him — the memory of my dead wife — and perverted it for perceived political gain," he wrote in the letter, which was published by The New York Times on Tuesday morning.
But Twitter made no commitment in its response: "We are deeply sorry about the pain these statements, and the attention they are drawing, are causing the family. We've been working to expand existing product features and policies so we can more effectively address things like this going forward, and we hope to have those changes in place shortly."
The new labels, first reported Tuesday afternoon, only showed up on Trump's tweets about mail-in ballots.
Twitter pushed back on multiple claims made by Trump in the tweets, calling them "unsubstantiated" in links attached to the labels. The links cited reporting by CNN, The Washington Post and other news outlets.
"Trump falsely claimed that California will send mail-in ballots to 'anyone living in the state, no matter who they are or how they got there.' In fact, only registered voters will receive ballots," the Twitter links said.
"Though Trump targeted California, mail-in ballots are already used in some states, including Oregon, Utah and Nebraska," the links said.
Trump's oldest son, Donald Trump Jr., responded to Twitter's move by asking – on Twitter – if the website is going to start "censoring & fact-checking all the numerous blue check mark 'journalists' & leftwing activists who falsely claimed that the Trump campaign colluded with the Russian government."
Trump has in recent weeks railed against some of the states offering mail-in voting services ahead of the 2020 election. He incorrectly claimed on Twitter last week that Michigan "illegally" mailed out nearly 8 million absentee ballots ahead of the state's primary.
"I will ask to hold up funding to Michigan if they want to go down this Voter Fraud path!" Trump tweeted.
In the Rose Garden on Tuesday afternoon, Trump claimed that Democrats are pushing for increased mail-in voting "because in theory, it is good for them."
Trump's critics have long called on Twitter to take action against Trump's use of the platform. Of the 18,000-plus false or misleading claims Trump has made as president, more than 3,300 of them were made in tweets, according to The Washington Post.
Twitter had unveiled the new warning labels in a May 11 blog post, though the tags were billed at the time as a tool to correct "disputed or misleading information related to COVID-19."
But the blog post noted that "moving forward, we may use these labels and warning messages to provide additional explanations or clarifications in situations where the risks of harm associated with a Tweet are less severe but where people may still be confused or misled by the content."