Facebook Inc said on Friday that it will start labelling newsworthy content that violates the social media company's policies, and label all posts and ads about voting with links to authoritative information, including those from politicians.

A Facebook spokeswoman confirmed the company's new policy would have covered a link on United States President Donald Trump's post about mail-in ballots last month, to which Facebook's smaller rival Twitter affixed a fact-checking label.

Chief Executive Mark Zuckerberg said in a live-streamed company town hall that Facebook would ban ads that claim people from groups based on race, religion, sexual orientation or immigration status are a threat to physical safety or health.

The policy change follows an advertising boycott campaign by several US civil rights groups pressuring the company to act on hate speech and misinformation gains traction.

Shares of Facebook and Twitter both fell more than seven percent on Friday after Unilever PLC said it would stop US ads on Facebook, Instagram and Twitter for the rest of the year, citing "divisiveness and hate speech during this polarized election period in the US."

Unilever, which owns brands like Dove soap and Lipton tea, and Japanese carmaker Honda Motor Co Ltd's US subsidiary both joined the growing ad boycott against Facebook as part of the "Stop Hate for Profit" campaign started after the death of George Floyd.

"Continuing to advertise on these platforms at this time would not add value to people and society," Unilever said in a statement.

The campaign specifically asks businesses not to advertise on Facebook's platforms in July, though Twitter has also long been urged to clean up alleged abuses and misinformation on its platform.

"We have developed policies and platform capabilities designed to protect and serve the public conversation, and as always, are committed to amplifying voices from underrepresented communities and marginalized groups," said Sarah Personette, vice president for Twitter's Global Client Solutions.

"We are respectful of our partners' decisions and will continue to work and communicate closely with them during this time."

More than 90 advertisers including Unilever's Ben & Jerry's, Verizon Communications Inc and The North Face, a unit of VF Corp, have joined the campaign, according to a list by ad activism group Sleeping Giants, a partner in the campaign.

In a statement, a Facebook spokeswoman pointed to its civil rights audit and investments in Artificial Intelligence that allow it to find and take action on hate speech.

"We know we have more work to do, and we'll continue to work with civil rights groups, GARM, and other experts to develop even more tools, technology and policies to continue this fight," she said, referring to the Global Alliance for Responsible Media.