Twitter has fact-checked a tweet by Donald Trump for the first time, leading the US President to accuse the social media company of interfering in the upcoming 2020 election.

On Tuesday Trump posted two tweets claiming that mail-in ballots would lead to an increase in fraudulent voting.

“There is NO WAY (ZERO!) that Mail-In Ballots will be anything less than substantially fraudulent. Mail boxes will be robbed, ballots will be forged and even illegally printed out and fraudulently signed. The Governor of California is sending ballots to millions of people, anything...living in the state, no matter why they are or how they go there, will get one,” Trump tweeted.

“That will be followed up with professionals telling all of these people, many of whom have never thought of voting before, how, and for whom, to vote. This will be a Rigged Election. No way!”

Hours later, Twitter updated these posts to include a link to a page saying the claims were “unsubstantiated” and had been fact-checked by a number of news organisations. The tweets now include a blue exclamation mark at the bottom with a prompt for readers to “get the facts about mail-in ballots”.

This links to a page with the headline: “Trump makes unsubstantiated claim that mail-in ballots will lead to voter fraud.”

Trump’s tweets included a number of false statements about in-mail ballots and California’s plan to expand its use of the system.

“These claims are unsubstantiated, according to CNN, Washington Post, and others. Experts say mail-in ballots are very rarely linked to voter fraud,” Twitter said.

This was done because Trump’s tweet violated Twitter’s “civic integrity policy”, a company spokesperson said.

This policy bans users from “manipulating or interfering in elections or other civic processes”.

A first time for everything

This is the first time that Twitter has applied its fact-checking function to a tweet by President Trump.

The service is an extension of the social media company’s new misleading information policy that it rolled out this month in an effort to address the prevalence of COVID-19 misinformation on the platform.

Trump quickly hit back at the feature, alleging it would interfere with the upcoming November election and repeated the same unsubstantiated claims.

“Twitter is now interfering in the 2020 Presidential Election,” he tweeted on Wednesday. “They are saying my statement on Mail-In Ballots, which will lead to massive corruption and fraud, is incorrect, based on fact-checking by Fake News CNN and the Amazon Washington Post.”

The fact check came just after Twitter had refused to take down a different tweet by Trump about the 2001 death of a former congressional staff member, despite her widower requesting the company do so because the post was furthering false claims.

According to Twitter, the mail-in ballot tweets were different because they related to election integrity.

Trump has more than 80 million followers on Twitter, with his posts regularly leading to controversy and calls for his account to be removed.

In October last year, Twitter clarified how it would deal with the accounts of controversial world leaders, saying they are “not above” the company’s policies but it will “err on the side” of leaving tweets online.

This followed a number of Democratic Presidential nominees criticising the company for allowing the president to freely post despite regularly breaching Twitter’s policies.

If a tweet by a world leader is reported, the company will assess it against its own rules, focusing on the language of the tweet rather than potential interpretations of it.

Even if it is found to be in violation of the rules, the tweet will remain online if there is a “clear public interest value” in it.