Twitter has flagged some of President Donald Trump’s tweets with a fact-check warning. On Tuesday, Twitter added a warning phrase to two Trump tweets that called mail-in ballots “fraudulent” and predicted that “mail boxes will be robbed,” among other things. Under the tweets, there is now a link reading “Get the facts about mail-in ballots” that guides users to a Twitter “moments” page with fact checks and news stories about Trump’s unsubstantiated claims.

Reacting to the development, Trump lashed out at Twitter and alleged that the social media platform is “now interfering in the 2020 Presidential Election.”  “Twitter is completely stifling Free Speech, and I, as President, will not allow it to happen,” Trump said. The move comes after years in which Twitter has declined to apply its community guidelines and other rules of the road to the 45th US president. It’s too soon to tell whether this action represents a turning point for Twitter in its treatment of Trump. But the warning labels suggest that the president has finally crossed a line that the company was not willing to move for him.