The battle focuses on a unique device identifier on every iPhone and iPad called the IDFA. Companies that sell mobile advertisements, including Facebook, use this ID to help target ads and estimate their effectiveness.
With a forthcoming update to iOS 14, each app that wants to use these identifiers will ask users to opt in to tracking when the app is first launched. If users opt out, it will make these ads a lot less effective. Facebook has warned investors that these looming changes could hurt its advertising business as soon as this quarter.
Facebook is testing the effects of this update now, before Apple makes it mandatory for all apps early this spring.
As part of this test, Facebook will begin showing some users its own prompts starting on Monday, explaining why it wants to track this activity and asking users to opt in. These prompts will appear on Apple users' screens immediately before the Apple pop-up appears.
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One test version of the Facebook prompt has a bold-faced header asking "Allow Facebook to use your app and website activity?" and claims that Facebook uses that information to "provide a better ads experience." It will then offer users a choice between "Don't Allow" and "Allow." (The precise language and appearance of the Facebook prompt may vary.)
No matter which selection users make on the Facebook prompt, if they choose not to allow tracking on the Apple pop-up, that choice will be final and Facebook will honor it.
Correction: An earlier version of this story misquoted a portion of Tim Cook's speech. The quote has been corrected.