Microblogging website Twitter for the first time took action against a series of tweets by United States President Donald Trump, labelling them with a warning sign and providing a link to further information, CNN reported.

Twitter added links to two of Trump’s tweets in which he had posted about mail-in ballots and falsely claimed that they would cause the November presidential election to be “rigged.”

The links – which were in blue lettering at the bottom of the posts and punctuated by an exclamation mark – urged people to “get the facts” about voting through mail. Clicking on the links lead to a CNN story that said Trump’s claims were unsubstantiated and to a curated fact-check page filled with further links and summaries of news articles debunking the assertion.

Twitter said Tuesday that Trump’s tweets about mail-in voting did not violate the company’s rules because they don’t explicitly discourage people from voting. But these Tweets contain “potentially misleading information” about voting processes and “have been labeled to provide additional context around mail-in ballots,” Twitter spokesperson Katie Rosborough told CNN. “This decision is in line with the approach we shared earlier this month.”

Under the company’s new policy , which was released on 11 May, Trump’s tweets violated Twitter’s “civic integrity policy”, which bars users from “manipulating or interfering in elections or other civic processes”, such as by posting misleading information that could dissuade people from participating in an election, according to The Guardian.

The changes immediately set off accusations from Trump that the company was biased against him. In a tweet, Trump claimed Twitter was “interfering in the 2020 Presidential Election” and added, in another post, that it was “completely stifling free speech”. “Federal law protects the rights of internet platforms to moderate the third-party speech they publish,” he added.

For years, Twitter has faced criticism over Trump’s posts on the social media platform, which he has used to threaten world leaders and spread falsehoods and misinformation. But Twitter has repeatedly said that the president’s messages did not violate its terms of service and that while Trump may have skirted the line of what was accepted under its rules, he never crossed it.

That changed on Tuesday after a severe backlash over tweets that Trump had posted about Lori Klausutis, a young woman who died in 2001 from complications of an undiagnosed heart condition while working for Joe Scarborough, a Florida congressman at the time. As part of his long-running feud with Scarborough, a host for MSNBC channel, Trump had posted false conspiracy theories about Klausutis’ death in recent days, suggesting that Scarborough was involved.

Twitter said it was “deeply sorry about the pain these statements” were causing the Klausutis family, but said that it would not remove Trump’s tweets because they did not violate its policies.

Over the weekend, the president issued several tweets calling into question the legality of mail-in-ballots. The storm of tweets followed Facebook and Twitter posts that wrongly claimed Michigan’s secretary of state mailed ballots to 7.7 million registered voters. Trump later deleted the tweet and posted an edited version that still threatened to hold up federal funds.

Twitter policy forbids sharing “false or misleading information intended to intimidate or dissuade people from participating in an election or other civic process.”