Apple could be required to permit competitors to run separate app stores on iPhones across Britain, after a decision from the market watchdog.
This would be a major shift to the company's well-known "walled garden" where apps can only be installed from the company's App Store.
But the UK competition watchdog has designated both Apple and Google as having "dominant market position" - indicating they have significant control over mobile platforms.
The regulator said the two companies "could be restricting innovation and competition".
But the authority emphasized it did not "determine or presume wrongdoing" from the companies.
"Mobile applications contributes 1.5% of the British economy and sustains around 400,000 jobs, which is why it's essential these markets function properly for enterprises," commented a top executive from the CMA.
Approximately ninety to one hundred percent of UK mobile devices operate using the two tech companies' operating systems, creating what the authority calls an "effective duopoly".
Based on current data, nearly half of UK mobile owners use an Apple device - which runs Apple's iOS - with the vast majority of the rest using Google's Android.
The CMA's investigation focused on how prominent Apple and Google's own apps are compared with rivals - as well as their browsers and platform software.
It is unknown what modifications the regulator will seek to implement, but previously it published guidelines detailing potential measures it could take.
These include requiring it to be easier for people to switch between iOS and Android phones, and for both firms to rank apps "fairly and openly" in their marketplaces.
Apple specifically may be compelled to allow third-party marketplaces on its devices, and let people to download programs straight from companies' websites.
This would mirror comparable regulations in the European Union, which previously took action against Apple for restrictive practices.
The technology firm warned the United Kingdom could lose access to getting new features - as has occurred in the EU - which the organization attributes to heavy regulation.
For example, some Apple Intelligence features which have been launched in other regions are not available in the EU.
"Apple faces intense rivalry in every sector where we operate, and we strive continuously to create the best products, services and user experience," the company said in a release.
"The UK's adoption of EU-style rules would weaken that, resulting in consumers with weaker privacy and security, delayed access to latest functions, and a divided, less seamless user journey."
Google device owners can presently use alternative marketplaces - though commentators say they are not as smooth as the company's official application marketplace.
The regulator's plan said the search company may have to "modify the interface" of downloading apps directly from online sources, as well as "remove user frictions" when using third-party platforms.
"There appears to be no the rationale for today's designation decision," a Google competition lead stated.
The representative said "the majority" of Google device owners use third-party platforms or download apps straight from a creator's site, and claimed there is a much wider selection of apps available for Android users versus those on Apple devices.
"Currently available are 24,000 Android phone models from 1,300 phone manufacturers worldwide, facing strong rivalry from iOS in the UK," the spokesperson continued.
Google's platform is an open-source operating system, which means creators can utilize and develop on top of it for no cost.
Google contends this means it promotes competition.
But consumer groups said curbs on these firms' dominance in other countries "currently assist businesses to innovate and giving customers more options".
"Their dominance is now creating genuine problems by restricting choice for consumers and market rivalry for companies," stated a consumer advocate.
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