A post by US President Donald Trump has been given a fact-check label by Twitter for the first time.
President Trump tweeted: "There is NO WAY (ZERO!) that Mail-In Ballots will be anything less than substantially fraudulent."
Twitter put a warning label under the post and a subsequent tweet under its new policy on misleading information.
Mr Trump has recently made several unsubstantiated claims about the validity of mail-in ballots.
Twitter's notification displays a blue exclamation mark underneath the tweets, suggesting readers "get the facts about mail-in ballots".
The social media company had pledged to increase the warning labels under false or misleading information on its site but it has been slow to take steps against the US president.
Twitter said the message "contain potentially misleading information about voting processes".
The company updated its policies on warning labels early this month.
The move comes on the heels of Twitter's decision not to remove comment President Trump made about the death of Lori Klausutis in 2001. The president has tweeted several messages promoting a conspiracy theory that Ms Klausutis was murdered by MSNBC host Joe Scarborough.
Her widower Timothy Klausutis asked Twitter to remove the post.
The company declined to take down those tweets but told Mr Klausutis it was "deeply sorry" about the pain caused by the president's statements.