The iPhone maker could be required to allow rivals to operate their own app stores on iPhones across Britain, after a ruling from the competition regulator.
This represents a major shift to the company's well-known "closed system" where apps can only be downloaded from the company's App Store.
But the UK competition watchdog has designated both Apple and Google as having "strategic market status" - effectively saying they have significant control over mobile platforms.
The regulator said the tech firms "could be restricting innovation and market rivalry".
But the regulator emphasized it did not "find or assume wrongdoing" from the firms.
"Mobile applications generates 1.5% of the UK's GDP and sustains around four hundred thousand positions, which is why it's essential these sectors work well for business," commented a top executive from the competition authority.
Approximately ninety to one hundred percent of British smartphones operate using Apple or Google's mobile platforms, creating what the authority calls an "effective duopoly".
Based on current data, 48.5% of UK mobile owners own an iPhone - which runs Apple's iOS - with the vast majority of the remaining users using the Android OS.
The CMA's investigation focused on how prominent the companies' own applications are compared with rivals - as well as their web applications and platform software.
It is unclear what changes the authority will look to request, but previously it published guidelines outlining potential measures it could take.
These comprise requiring it to be easier for people to transition between iOS and Android devices, and for both firms to list applications "in a fair, objective and transparent manner" in their app stores.
The Cupertino company particularly may be compelled to permit third-party marketplaces on its products, and enable people to download programs straight from developer sites.
This would follow comparable regulations in the EU, which previously took action against Apple for anti-competitive behaviour.
Apple warned the UK could lose access to receiving updates - as has happened in the EU - which the organization attributes to strict rules.
For instance, some AI features which have been rolled out in other parts of the world are not accessible in the EU.
"We encounters fierce competition in every market where we do business, and we strive continuously to create the best products, solutions and user experience," the organization said in a statement.
"Britain's implementation of European regulations would undermine that, leaving users with reduced data protection and safety, delayed access to new features, and a fragmented, more complicated user journey."
Android users can presently use alternative marketplaces - though critics say they are not as user-friendly as the company's official Play Store.
The CMA's roadmap said the search company may have to "modify the interface" of downloading apps straight from online sources, as well as "remove user frictions" when using third-party platforms.
"We simply do not see the justification for the current classification," a Google policy executive remarked.
The executive said "most" of Android users use third-party platforms or install applications straight from a creator's site, and asserted there is a far greater range of apps available for Android users versus those on Apple devices.
"There are now twenty-four thousand Google-compatible devices from 1,300 phone manufacturers globally, facing strong rivalry from iOS in the United Kingdom," the spokesperson added.
Google's platform is an open-source operating system, which means developers can utilize and develop on top of it for free.
The company contends this means it promotes competition.
But advocacy organizations said restrictions on these firms' dominance in different nations "currently assist businesses to develop and giving consumers more choice".
"Their dominance is now creating genuine problems by restricting choice for users and competition for companies," commented a consumer advocate.
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