Tests found that revenue from the Audience Network platform that lets Facebook's system work behind the scenes to target ads in apps fell by more than half when personalisation was thwarted, an online post explained.
"In reality, the impact to Audience Network on iOS 14 may be much more, so we are working on short-and long-term strategies to support publishers through these changes," Facebook said.
"Ultimately, despite our best efforts, Apple's updates may render Audience Network so ineffective on iOS 14 that it may not make sense to offer it on iOS 14."
Apple is expected to release the new version of its mobile operating system later this year, and developers will have the option from the outset to ask users for permission when it comes to tracking.
"We understand that iOS 14 will hurt many of our developers and publishers at an already difficult time for businesses," Facebook said.
The social networking giant's system will still be able to target ads in apps made for Android-powered smartphones or tablets, Facebook said.
Apple, which does not rely on digital ad revenue, has been working to limit tracking of online activity and has stressed user privacy as a priority.
"We believe technology should protect users' fundamental right to privacy," Apple said.
"That means giving users tools to understand which apps and websites may be sharing their data with other companies for advertising or advertising measurement purposes, as well as the tools to revoke permission for this tracking."