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

The president can't unilaterally regulate or close the companies, which would require action by Congress or the Federal Communications Commission. But that didn't stop Trump from issuing angry warnings.

Claiming tech giants “silence conservative voices,” Trump tweeted early Wednesday, “We will strongly regulate, or close them down, before we can ever allow this to happen.” Later he tweeted “Big Action to follow.”

He repeated his unsubstantiated claim that expanding mail-in voting “would be a free for all on cheating, forgery and the theft of Ballots.”

There was no immediate reaction from Twitter or other social media companies to the 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 “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.

Trump replied on Twitter, accusing the platform of “interfering in the 2020 Presidential Election” and insisting that “as president, I will not allow this to happen.” His 2020 campaign manager, Brad Parscale, said Twitter's “clear political bias” had led the campaign to pull “all our advertising from Twitter months ago.” Twitter has banned all political advertising since last November.