Twitter on Tuesday slapped a fact-check label on President Trump’s tweets for the first time, a response to long-standing criticism that the company is too hands-off when it comes to policing misinformation and falsehoods from world leaders.

The move, which escalates tensions between Washington and Silicon Valley in an election year, was made in response to two Trump tweets over the past 24 hours. The tweets falsely claimed that mail-in ballots are fraudulent. Twitter’s label says, “Get the facts about mail-in ballots,” and redirects users to news articles about Trump’s unsubstantiated claim.