More and more iPhone apps are offering people the option of signing up by using information stored with Apple, adding to the array of quick sign-in formats that let people skip typing in their email address and other details. But how Apple is implementing this option—requiring it on all apps that offer sign-in options from other firms like Google or Facebook—has upset some developers. And that has prompted complaints that the U.S. Department of Justice is now investigating, said two people with direct knowledge of the situation.

Apple says its “Sign in with Apple” button, which gives users the ability to hide their personal details from the app, is “pro privacy.” But investigators are examining how Apple uses the sign-in button and other App Store rules to make it more difficult for users to switch to a rival device maker, according to the two people, who have met regularly with the Justice Department over the past 18 months. The government’s interest in the Apple sign-in button, which the company introduced in 2019, hasn’t been previously reported.