The measures were due to arrive in the latest iOS 14 update in the autumn.
But Apple said the changes were being delayed until the start of 2021 to give app developers and websites more time to adapt their services.
Facebook has warned that Apple's privacy plan could make one of its advertising tools "so ineffective on iOS 14 that it may not make sense to offer it on iOS 14".
The social network says it will no longer collect users' ad-tracking IDs on iOS 14, and that Apple's plan had forced it to make that decision.
What is Apple changing?Apple devices including the iPhone, iPad and Apple TV box have a unique ID known as the "identifier for advertisers" (IDAF).
It can help apps monitor the effectiveness of an advertising campaign. For example, it can help determine whether somebody downloaded an app after seeing an ad.
Android has a similar tool known as the Android Advertising ID (AAID).Apple already lets people switch off access to their IDAF on iOS.
However, once the change is implemented in 2021, it will be off by default and advertisers will have to ask permission to access it.
Apps will also have to ask permission to track what people do in apps and on websites owned by other companies.Additionally, when iOS 14 is released in the autumn, apps will have to declare what data they collect and how they track people in Apple's App Store.
Another new security feature will highlight when an app accesses information on the user's clipboard.
What else is changing?
One of the biggest changes to the iPhone's iOS 14 operating system will be a shake-up of the home screen.
Apple is updating its "widgets" - blocks that display a stripped-down, small app window - so that they can be placed among the icons for other programs.
- Read more:New features coming to iOS 14
Apple is releasing a new API to allow developers to add the new sign-in function to their apps for a more convenient way of logging in using Face ID without revealing additional personal information. The new sign-in feature is coming with Apple's new operating systems this fall and will be available across macOS, iOS, and through websites.
For the first time, users will be able to set third-party email and web-browser apps as the default in iOS, rather than Apple's own software.
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