President Trump on Tuesday accused Twitter of “interfering in the 2020 presidential election” after the social media giant fact-checked his claim that mail-in ballots lead to widespread fraud. “They are saying my statement on Mail-In Ballots, which will lead to massive corruption and fraud, is incorrect, based on fact-checking by Fake News CNN,” the president tweeted. He went on to accuse the company of “stifling free speech” and declared that “as president,” he will “not allow it to happen.” The president's outburst came after Twitter added fact-checking labels to two of his tweets Tuesday, both claiming without evidence that any voting by mail in the United States would invite widespread fraud.

It’s the first time the social network has taken action against the commander-in-chief’s remarks in his favorite forum. “There is NO WAY (ZERO!) that Mail-In Ballots will be anything less than substantially fraudulent,” the president wrote, taking aim at California, which plans to send millions of mail-in ballots to residents. Twitter’s corresponding label read, “Get the facts about mail-in ballots” and led to a Twitter Moment headlined, “Trump makes unsubstantiated claim that mail-in ballots will lead to voter fraud” that cited CNN, The Washington Post, and other news outlets.

The tete-a-tete comes the same day Trump promoted a baseless conspiracy theory that talk show host Joe Scarborough had killed a staffer. Twitter said it would not remove those tweets.