Apple’s new privacy feature requiring developers ask for permission to track iOS users for ad targeting is at last going live in the next iOS 14 beta with a planned full release some time this spring for non-beta users, the company tells The Verge.

The announcement coincides with Data Privacy Day, as well as a speech on privacy from Apple CEO Tim Cook later today at the Computers, Privacy and Data Protection conference in Brussels. Apple initially planned for the feature to go live with the launch of iOS 14 last fall, but it delayed its implementation to 2021 in September of last year to give developers more time to comply. Today’s announcement narrows the launch window to this spring, but Apple is not commenting further on when exactly we might see it to go live for everyone.

Called App Tracking Transparency, the new opt-in requirement will mark a significant shift in how mobile app developers are able to collect data on iPhone owners and share that data with other firms to aid in advertising. Prior to the change, Apple let iPhone owners dig into their settings to disable this type of tracking. Now, instead of forcing users to be proactive about disabling it, Apple will demand developers ask for permission or risk suspension or removal from the App Store if they don’t comply or try to skirt the rules.

The primary way advertisers are able to, say, know when you are shopping for a new hat on one app before serving you ads for that same hat on another app is that a unique identifying code, the so-called Identifier for Advertisers (IDFA), is linked to your device, collected by the first app, and shared with the second. That allows those apps to serve targeted ads and to measure whether the ad actually worked, for instance if you ended up purchasing that hat you saw in an Instagram ad by clicking an ad for the company’s online store in Google Chrome.

Apple’s new opt-in requirement will make it so developers must have express consent from iOS device owners to allow their IDFA to be collected and shared across apps. App makers can still use other information you give them for the purpose of targeting advertising even if you opt not to let the app track you, but that information cannot be shared with another company for the purpose of ad tracking under Apple’s new policy. The sharing with other third-party companies is effectively what Apple refers to when it uses the word “tracking.”

Apple intends to strictly police any attempt to get around the opt-in requirement. For instance, it says app developers will not be allowed to disable app functionality of any kind if users say no to the opt-in, and that developers will also be barred from charging money or incentivizing users with in-app perks or giveaways to sway their decision one way or the other. Any app that tries to replace the IDFA with another identifying piece of information, like an email address, will be in violation of the opt-in requirement.

Apple says the rules will also apply to its own apps, and the company already lets users disable personalized advertising the company serves within the App Store, Apple News, and the Stocks app using data it collects from your device. (It’s worth noting that ad personalization is not the same as ad tracking, and mobile app companies can still personalize ads so long as they can disclose that with an App Store privacy label.) Apple has no history of sharing the information it collects with other companies, either, and it makes that clear in its ad personalization toggle in the iOS settings.

This is expected to affect both the companies that run ad networks, like Facebook, and the companies paying for the ads, like the aforementioned unnamed hat seller. That’s precisely why Facebook has come out as arguably the biggest opponent to Apple’s new privacy measures, which include not only this new opt-in requirement but also app privacy labels it launched on the App Store last month.

Facebook has positioned itself as a champion of small businesses that risk getting hurt by this privacy change, and small businesses do rely on Facebook’s ad network and its powerful targeting tools to reach customers. Past privacy changes to Apple’s mobile Safari browser did also have legitimate negative consequences for ad-supported businesses like news websites. (The Verge is an ad-supported news website.)

But in full-page newspaper ads and statements to the press, Facebook has gone a step further and cast Apple as a hypocrite trying to exempt itself from the rules it forces on other developers and as greedy for encouraging app business models that rely less on advertising and more on subscriptions, of which Apple would theoretically get a cut.

“Apple has every incentive to use their dominant platform position to interfere with how our apps and other apps work, which they regularly do to preference their own,” Facebook CEO Mark Zuckerberg said on an earnings call on Wednesday. “This impacts the growth of millions of businesses around the world, including with the upcoming iOS 14 changes.” Zuckerberg added that, “Apple may say they’re doing this to help people but the moves clearly track their competitor interests.”

Apple has consistently defended its choice as a way to give users more freedom over their privacy and refuted Facebook’s claims it intends to hold its first-party software to different standards. The showdown has emerged as one of the largest and most visible tech company feuds in recent memory, though it’s clear now Facebook has little to no leverage in the situation despite its defensiveness and public posturing. The changes are imminent, and Facebook will be forced to comply as it was with the privacy labels last month.

To further hammer home its privacy philosophy, Apple has created a new online guide it’s calling “A Day in the Life of Your Data” that breaks down common ad tracking and targeting practices in the mobile app and web industries and presents statistics on the prevalence of these practices. Apple says the average mobile app contains six trackers that share your data with other apps, and that a “large and opaque industry has been amassing increasing amounts of personal data.”

“A complex ecosystem of websites, apps, social media companies, data brokers, and ad tech firms track users online and offline, harvesting their personal data. This data is pieced together, shared, aggregated, and monetized, fueling a $227 billion-a-year industry,” the guide reads. “This occurs every day, as people go about their daily lives, often without their knowledge or permission.”