Facebook has made a mint by enabling advertisers to identify and reach the very people most likely to react to their messages. Ad buyers can select audiences based on details like a user’s location, political leanings and interests as specific as the Museum of the Confederacy or online gambling. And they can aim their ads at as few as 20 of the 1.5 billion daily users of the social network.

Brands love it. So do political campaigns, like those for President Trump and former President Barack Obama, which tailored their messages to narrow subsets of voters.

But microtargeting, as the technique is called, is coming under increased scrutiny in the United States and Europe. Some government officials, researchers and advertising executives warn that it can be exploited to polarize and manipulate voters. And they are calling for restrictions on its use in politics, even after Facebook, in response to criticism, recently limited some of the targeting categories available to advertisers.

“It has essentially weaponized ad technology designed for consumer products and services,” said Sarah Golding, the president of the Institute of Practitioners in Advertising, an industry organization in Britain. Her group recently called for a moratorium on political microtargeting. “There is a danger that every single person can get their own concerns played back to them,” she said.