Apple plans to delay the enforcement of a controversial change to its next mobile operating system that would upend how ads are targeted on iPhones and iPads, according to people familiar with the matter.

The change in iOS 14, the next version of Apple’s mobile software, will require developers to ask users to share their device’s unique identifier for advertising purposes through a prompt. Many developers and advertisers rely on this identifier, or IDFA, to track the effectiveness of their ad campaigns in mobile apps, particularly for ads that prompt the viewer to download a specific app or game. Experts believe most people will not agree to share their IDFA when asked.