The iPhone maker could be required to allow rivals to run separate app stores on Apple devices in the UK, after a decision from the competition regulator.
This would be a major shift to Apple's well-known "closed system" where applications can only be downloaded from its own App Store.
But the Competition and Markets Authority has classified both the tech giants as having "strategic market status" - indicating they have a lot of power over mobile platforms.
The regulator said the tech firms "could be restricting progress and market rivalry".
But the regulator clarified it did not "determine or presume misconduct" from the firms.
"The app economy contributes one and a half percent of the UK's GDP and supports around four hundred thousand positions, which is why it's crucial these markets work well for enterprises," stated a senior official from the competition authority.
Around ninety to one hundred percent of UK mobile devices operate using the two tech companies' mobile platforms, creating what the regulator calls an "virtual monopoly".
Based on recent analysis, 48.5% of British smartphone users own an Apple device - which runs Apple's iOS - with the vast majority of the remaining users using the Android OS.
The regulatory probe examined how dominant the companies' own apps are versus competitors - as well as their browsers and platform software.
It is unknown what modifications the regulator will seek to implement, but earlier it published roadmaps outlining possible actions it could take.
These include mandating it to be more straightforward for people to transition between iOS and Android phones, and for both firms to list applications "fairly and openly" in their marketplaces.
The Cupertino company specifically may be compelled to permit alternative app stores on its devices, and let people to install apps directly from developer sites.
This would mirror comparable regulations in the EU, which previously took action against Apple for anti-competitive behaviour.
The technology firm cautioned the United Kingdom could lose access to receiving updates - as has occurred in the EU - which the company attributes to strict rules.
For instance, some AI features which have been rolled out in other regions are not available in the EU.
"Apple encounters intense rivalry in every market where we do business, and we strive continuously to create the best products, solutions and user experience," the company said in a statement.
"The UK's adoption of European regulations would weaken that, resulting in consumers with reduced data protection and security, delayed access to new features, and a fragmented, more complicated user journey."
Google device owners can currently use third-party app stores - though critics say they are not as user-friendly as the company's official application marketplace.
The regulator's plan said Google may have to "modify the interface" of installing applications directly from online sources, as well as "eliminate barriers" when using third-party platforms.
"There appears to be no the justification for today's designation decision," a company competition lead stated.
The executive said "the majority" of Android users use alternative app stores or download apps directly from a developer's website, and asserted there is a far greater range of apps offered for Google device owners compared to those on Apple devices.
"There are now twenty-four thousand Android phone models from 1,300 phone manufacturers globally, facing strong rivalry from Apple's platform in the UK," the spokesperson added.
Google's platform is an open-source operating system, which means developers can use and build on top of it for free.
The company contends this means it promotes competition.
But consumer groups said restrictions on these companies' power in different nations "are already helping businesses to develop and providing customers more choice".
"The companies' control is now creating genuine problems by restricting choice for consumers and market rivalry for companies," stated a policy expert.
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