By Dave Sebastian

Facebook Inc. Chief Executive Mark Zuckerberg backed his stance of largely not interfering with politicians' posts on the company's platform as President Trump is expected to sign an executive order that would make it easier for regulators to hold social-media companies liable for curbing users' speech.

"I don't think Facebook or internet platforms in general should be arbiters of truth," Mr. Zuckerberg said in a CNBC interview aired Thursday. "I think that's kind of a dangerous line to get to in terms of deciding what is true and what isn't."

The order would seek to limit the broad legal protection that federal law currently provides social-media companies and other online platforms, The Wall Street Journal reported Wednesday.

Facebook's policy is to not fact-check speech or advertising by politicians, though it uses third-party fact checkers to identify potentially false stories. Mr. Zuckerberg has been battling a chorus of critics for misinformation, privacy violations and more. He has defended the policy as a commitment to free expression.

Mr. Zuckerberg said the company will take down content that is perceived to be harmful, such as that advocating for a cure to a disease that hasn't been proven. Facebook took down in late March a post by Brazilian President Jair Bolsonaro that said hydroxychloroquine, an antimalaria drug, was an effective treatment for Covid-19.

But Mr. Zuckerberg also reiterated that the company isn't in the business of determining what is true or false.

"In general, you want to give as wide of a voice as possible, and I think you want to have a special deference to political speech," he said.

Twitter Inc.'s move earlier this week to apply for the first time fact-checking notices to two tweets from Mr. Trump drew the ire of the president. "Twitter is completely stifling FREE SPEECH, and I, as President, will not allow it to happen!" he wrote in a tweet. The president had tweeted about the potential for fraud involving mail-in ballots.

"This does not make us an 'arbiter of truth,'" Twitter CEO Jack Dorsey said in a tweet on Wednesday, referring to the company's move to apply the fact-checking label to Mr. Trump's content. "Our intention is to connect the dots of conflicting statements and show the information in dispute so people can judge for themselves."

Current federal legal protections for social-media companies were adopted by Congress in Section 230 of the 1996 Communications Decency Act. The law gives online companies broad immunity from liability for their users' actions, as well as wide latitude to police content on their sites.

Write to Dave Sebastian at dave.sebastian@wsj.com