The iPhone maker may have to allow rivals to operate separate app stores on iPhones in the UK, following a ruling from the competition regulator.
This would be a major shift to the company's infamous "walled garden" where apps can only be downloaded 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 a lot of power over mobile platforms.
The CMA said the two companies "may be limiting innovation and market rivalry".
But the authority clarified it did not "find or assume wrongdoing" from the companies.
"The app economy generates one and a half percent of the UK's GDP and supports around four hundred thousand positions, which is why it's essential these markets work well for business," stated a senior official from the CMA.
Approximately ninety to one hundred percent of British smartphones run on Apple or Google's operating systems, creating what the regulator calls an "virtual monopoly".
Based on current data, nearly half of British smartphone users use 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 Apple and Google's own applications are versus rivals - as well as their web applications and platform software.
It is unknown what changes the authority will look to request, but previously it published guidelines detailing potential measures it could take.
These comprise mandating it to be more straightforward for people to switch between iOS and Android devices, and for both companies to list applications "fairly and openly" in their marketplaces.
Apple particularly may be required to permit third-party marketplaces on its products, and let people to install apps directly from companies' websites.
This would follow a similar ruling in the European Union, which previously took action against Apple for restrictive practices.
Apple warned the United Kingdom could face delays to getting new features - as has happened in the European Union - which the company attributes to strict rules.
For instance, some AI capabilities which have been rolled out in other regions are not accessible in the EU.
"We faces fierce competition in every sector where we do business, and we work tirelessly to create the best products, services and customer interface," the company said in a statement.
"The UK's adoption of European regulations would undermine that, resulting in consumers with weaker privacy and security, slower availability to new features, and a divided, less seamless experience."
Android users can currently use third-party app stores - though critics say they are not as smooth as Google's own application marketplace.
The regulator's plan said Google may have to "modify the interface" of downloading apps directly from websites, as well as "eliminate barriers" when using third-party platforms.
"There appears to be no the rationale for the current classification," a company policy executive remarked.
The representative said "most" of Google device owners use alternative app stores or install applications 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 iOS products.
"Currently available are 24,000 Android phone models from 1,300 phone manufacturers worldwide, facing intense competition from iOS in the United Kingdom," the representative added.
Google's platform is an open-source operating system, which means developers can use and build on top of it for free.
Google argues this means it promotes market competition.
But consumer groups said restrictions on these firms' dominance in different nations "are already helping enterprises to develop and providing customers more options".
"Their dominance is now creating genuine problems by limiting options for consumers and competition for companies," commented a consumer advocate.
A seasoned digital marketer and web developer with over a decade of experience in the UK tech industry.