The iPhone maker may have to permit competitors to run separate application platforms on iPhones in the UK, after a decision from the competition regulator.
This would be a major shift to the company's well-known "closed system" where applications can only be installed from the company's App Store.
But the UK competition watchdog has classified both the tech giants as having "strategic market status" - indicating they have significant control over mobile platforms.
The regulator said the tech firms "could be restricting progress and market rivalry".
But the authority emphasized it did not "determine or presume wrongdoing" from the firms.
"The app economy contributes 1.5% of the British economy and sustains around 400,000 jobs, which is why it's essential these markets work well for business," commented a top executive from the competition authority.
Approximately 90-100% of British smartphones run on the two tech companies' mobile platforms, creating what the authority calls an "effective duopoly".
Based on recent analysis, nearly half of British smartphone users own an Apple device - which runs Apple's iOS - with the overwhelming bulk of the remaining users using Google's Android.
The regulatory probe examined how dominant Apple and Google's own apps are versus rivals - as well as their web applications and operating systems.
It is unknown what modifications the authority will seek to implement, but earlier it published guidelines detailing possible actions it could take.
These comprise mandating it to be more straightforward for people to switch between Apple and Android phones, and for both companies to list applications "fairly and openly" in their marketplaces.
Apple particularly may be compelled to permit third-party marketplaces on its products, and let people to download programs straight from developer sites.
This would mirror comparable regulations in the European Union, which previously took action against the company for restrictive practices.
The technology firm cautioned the United Kingdom could lose access to getting new features - as has happened in the European Union - which the company attributes to heavy regulation.
For instance, some AI capabilities which have been rolled out in other regions are not available in the European market.
"We encounters intense rivalry in every sector where we operate, 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 weaken that, leaving users with weaker privacy and security, slower availability to new features, and a fragmented, less seamless user journey."
Google device owners can presently use third-party app stores - though critics say they are not as smooth as the company's official Play Store.
The regulator's plan said the search company may have to "modify the interface" of downloading apps straight from websites, as well as "eliminate barriers" when using alternative app stores.
"There appears to be no the justification for today's designation decision," a Google policy executive stated.
The representative said "the majority" of Google device owners use third-party platforms or install applications straight from a developer's website, and claimed there is a much wider selection of apps available for Google device owners compared to those on Apple devices.
"There are now twenty-four thousand Android phone models from thirteen hundred device makers globally, facing intense competition from Apple's platform in the United Kingdom," the spokesperson continued.
Android is an freely available software, which means creators can utilize and develop on top of it for free.
Google argues this means it opens up market competition.
But consumer groups said restrictions on these companies' power in different nations "are already helping businesses to innovate and providing customers more choice".
"The companies' control is now creating genuine problems by restricting choice for consumers and competition for businesses," commented a consumer advocate.
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