President Donald Trump on Wednesday threatened social media companies with new regulations or even shuttering after Twitter added fact checks to two of his tweets.

There was no immediate reaction from Twitter or other social media companies to the president’s threats.

Trump and his campaign had lashed out Tuesday after Twitter added a warning phrase to two Trump tweets that called mail-in ballots “fraudulent” and predicted that “mailboxes 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.

But some Trump allies, who have alleged bias on the part of tech companies, have questioned whether platforms like Twitter and Facebook should continue to enjoy liability protections as “platforms” under federal law — or be treated more like publishers, which can face lawsuits over content.