“When millions of voters will be making their decisions, the president will be silenced by the Silicon Valley mafia, who will at the same time allow corporate media to run their biased ads to swing voters in key states,” said Samantha Zager, a Trump campaign spokeswoman.
Hours after rolling out its changes, Facebook applied its new rules to one of Mr. Trump’s posts on his Facebook page, in which he cast doubt on the vote-by-mail process. The company added a warning label that read, “Voting by mail has a long history of trustworthiness in the U.S. and the same is predicted this year.”
Mr. Biden’s campaign didn’t immediately return a request for comment.
Other social media companies, including YouTube and Twitter, have also moved to minimize political manipulation on their platforms. Twitter banned political advertising last year and has added labels to politicians’ tweets. On Thursday, Twitter also added a label to the tweet sent by Mr. Trump about voting that echoed his language on Facebook. YouTube has confirmed that it was holding conversations on postelection strategy, but has declined to elaborate.
Facebook, a key battleground for both presidential campaigns, has been most in the eye because of its billions of users. It has faced increasing scrutiny in recent months as domestic misinformation about this year’s election has proliferated. Yet Mr. Zuckerberg has declined to remove much of that false information, saying that Facebook supports free speech and that politicians’ posts are newsworthy. Many of the company’s own employees have objected to that position.
On Tuesday, Facebook said the Kremlin-backed group that interfered in the 2016 presidential election, the Internet Research Agency, had tried to meddle on its service again using fake accounts and a website set up to look like a left-wing news site. Facebook, which was warned by the Federal Bureau of Investigation about the Russian effort, said it had removed the fake accounts and news site before they gained much traction.
In his post, Mr. Zuckerberg said Facebook had removed over 100 networks worldwide in the last four years that were trying to influence elections. But increasingly, the threats to undermine the legitimacy of the November election were coming “from within our own borders,” he said.
As a result, Facebook said, it will begin barring politicians from placing new ads on Facebook and Instagram, the photo-sharing service it owns, on Oct. 27. Existing political ads will not be affected. Political candidates will still be able to adjust both the groups of people their existing ads are targeting and the amount of money they spend on those ads. They can resume running new political ads after Election Day, the company said.