President-elect Donald J. Trump and his allies have vowed to squash an online “censorship cartel” of social media firms that they say targets conservatives.

Already, the president-elect’s newly chosen regulators at the Federal Communications Commission and the Federal Trade Commission have outlined plans to stop social media platforms like Facebook and YouTube from removing content the companies deem offensive — and punish advertisers that leave less restrictive platforms like X in protest of the lack of moderation.

“The censorship and advertising boycott cartel must end now!” Elon Musk, the owner of X, whom Mr. Trump has appointed to cut the federal budget, posted on his site last month.

In Europe, social media companies face the opposite problem. There, regulators accuse the platforms of being too lax about the information they host, including allowing posts that stoked political violence in Britain and spread hate in Germany and France.

Mr. Trump’s return to the White House is expected to widen the speech divide that has long existed between the United States and Europe, setting up parallel regulatory systems that tech policy experts say could influence elections, public health and public discourse. That’s putting social media companies in the middle of a global tug of war over how to police content on their sites.

“What you are seeing is conflicting laws emerging from the world’s democracies, and consumers in the end suffer,” said Kate Klonick, an associate professor of property and internet law at St. John’s University School of Law. The result could be a fractured internet experience where people see different content based on the laws where they live, she said.