One of President Donald Trump’s tweets has been given a fact-check label by Twitter for the first time.

President Trump tweeted, without providing evidence: “There is NO WAY (ZERO!) that Mail-In Ballots will be anything less than substantially fraudulent.”

Twitter put a warning label in the president’s post and linked to a page that described the claims as “unsubstantiated”.

On May 27, President Trump threatened to “strongly regulate” or even “close down” social media platforms.

He tweeted to his 80 million followers that Republicans felt the platforms “totally silence conservatives” and that he would not allow this to happen. In an earlier tweet, the president said that Twitter was “completely stifling free speech”.

Later on May 27 President Trump said that Twitter “has now shown everything we have been saying about them… is correct” and vowed “big action to follow”.

It is unclear what regulatory steps the president could take without new laws passed by Congress. The White House has yet to offer further details.

For years, Twitter has faced criticism for not acting on Donald Trump’s controversial tweets, which include personal attacks on political rivals and debunked conspiracy theories.

This month Twitter introduced a new policy on misleading information amid the coronavirus pandemic.

However, President Trump’s recent posts promoting a conspiracy theory about the death of political aide Lori Klausutis, blaming a high-profile critic, have not received the same treatment.

The notification on President Trump’s tweet shows a blue exclamation mark and a link suggesting readers “get the facts about mail-in ballots”.

The link directs users to a page on which the president’s claims are described as “unsubstantiated”, citing reporting by CNN, the Washington Post and others.

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The pandemic is putting pressure on American states to expand the use of postal voting because people are worried about becoming infected at polling stations.

In a “what you need to know” section, Twitter writes that President Trump “falsely claimed mail-in ballots would lead to ‘a Rigged Election’.”

Twitter had pledged to increase the use of warning labels about false or misleading information on its site, but has been slow to take steps against President Trump.

President Trump posted the same claim about mail-in ballots on Facebook, but it is not fact-checked on that platform.

With more than 52,000 tweets currently to his name, the president is a prolific tweeter and relies on the platform to disseminate his views to millions of people.

President Trump has used Twitter to launch attacks on opponents, with targets ranging from North Korean leader Kim Jong-un to his political rivals in the US.