U.S. President Donald Trump early on Wednesday morning threatened to “strongly regulate” or shut down social media platforms after Twitter fact-checked him for the first time.

Republicans feel that Social Media Platforms totally silence conservatives voices. We will strongly regulate, or close them down, before we can ever allow this to happen. We saw what they attempted to do, and failed, in 2016. We can’t let a more sophisticated version of that….

— Donald J. Trump (@realDonaldTrump) May 27, 2020

The president accused social media platforms of silencing “conservative voices,” a charge that has been leveled against other platforms like Facebook.

“We will strongly regulate, or close them down, before we can ever allow this to happen,” Trump said, later adding, “Social Media. Clean up your act, NOW!!!!”

The U.S. President does not have the power to unilaterally shut down a company.

On Tuesday, the President sent out a tweet claiming that instituting a mail-in ballot system for voting in the U.S. would lead to widespread voter fraud, a charge that has no data to support it.

Twitter attached a fact-check message to Trump’s tweet allowing users to “Get the facts about mail-in ballots.” The link leads to a fact-checking page that describes Trump’s mail-in voting claim as “unsubstantiated.”

Twitter had been rolling out fact-checking mainly for coronavirus misinformation. Before Tuesday, it had never attached such a notice to one of Trump’s tweets.

The notion of regulating social media platforms has been a question for lawmakers since the 2016 election after various platforms were accused of fomenting divisive politics and proliferating of inaccurate statements.

Tech leaders pushed back against Trump’s threat Wednesday. Information Technology and Innovation Foundation vice president Daniel Castro said the president was “mistaken.”

“Social media does not have an anti-conservative bias. Social media provides a valuable platform for voices across the political spectrum to share ideas and information,” Castro said. “Online misinformation is a serious problem, and social media companies have rightfully stepped up to address the problem in partnership with civil society and governments around the world. While there may be occasional missteps, the private sector has shown a tremendous commitment to addressing this problem in a fair and transparent manner.”