In the upcoming iOS 14, apps must explicitly ask users for permission to collect and share data, which means ads will no longer be able to "follow" users on apps outside of Facebook.
Users targeted in this way are eight times more likely to purchase products, according to Facebook.
But iOS 14 tests suggest "more than 50% drop in ... publisher revenue."
"Far-reaching impact"
Audience Network, which Facebook describes as a "way for advertisers to extend their campaigns beyond Facebook and into other mobile apps", works by using an identifier to target advertising based on user "likes" and preferences.
IPhone users can already turn off this tracking.
But Apple's plan to require all users to actively join before they can be tracked "could make Audience Network so ineffective on iOS 14 that it might not make sense to offer it," Facebook said.
In a blog, Facebook warned advertisers that "they should expect their ability to monetize effectively from Audience Network to decline" and called for an industry consultation on the changes, which it believes would have "a far-reaching impact on the ecosystem of developers ".