Campaign group says excessive profits cost UK users £4bn a year.
The UK's Competition and Markets Authority (CMA) is investigating further action against mobile giants Apple and Google, as part of a fresh push to potentially limit their app store dominance.
Today, the CMA launched its new investigation and announced its first step: a consultation on whether to designate the two companies as having key Stategic Market Status (SMS).
This label would grant the authority fresh powers to intervene in how Apple and Google's mobile operating systems and app stores are run, using powers granted by last year's Digital Markets, Competition and Consumer Act.
For now, the CMA has begun an "invitation to comment" phase, which lasts until 12th February. This involves seeking responses from individuals, groups and businesses on their views of how Apple and Google's mobile ecosystems are run.
The CMA's conditions for labelling a company as an SNS rest on whether it meets at least one of three conditions: having a UK turnover of more than £1bn (or a global turnover of £25bn), having "substantial and entrenched market power", and having "a position of strategic significance" that sees it able to substantially influence how other firms behave.
Eurogamer has contacted Apple and Google for comment.
The Coalition for App Fairness, a group backed by Fortnite maker Epic Games, as well as the companies behind Spotify, Tinder and Checkatrade, responded positively to today's news.
"We welcome today's consultation from the CMA, the first step in ensuring Apple and Google are finally held accountable for their market dominance," reads a statement from the Coalition for App Fairness sent to Eurogamer.
"Extensive CMA investigations have revealed the real harm being caused by these monopolistic practices - excess profits made by Apple and Google in mobile app ecosystems are costing UK consumers £4bn a year.
"We look forward to working with the CMA to deliver strong, clear rules that will finally require these gatekeepers to play fair, creating genuine competition that benefits everyone."
Epic Games launched its own mobile app store last year worldwide on Android devices, and on iOS in the European Union - where legislation forces Apple to allow competing app stores to operate.
The company behind Fortnite is keen to gain its own foothold on both platforms after being kicked off both the Apple App Store and Google Play previously for deliberately breaking their store terms - something which company boss Tim Sweeney said had cost Epic Games around $1bn and has consistently complained that it must jump through hoops on both Apple and Google ecosystems, as it attempts to launch a rival shop front that disrupts their dominance.
Earlier this month, the CMA first announced plans to investigate whether Google, which it says accounts for more than 90 percent of all search queries within the UK, should be labelled with SMS status for its search and search advertising services.
If the CMA decides either company should be designated with SMS status, the authority states that it will be able to "guide the behaviour" of each firm, "tackling conduct that could undermine fair competition, or exploit people and businesses".
Direct action could be taken through "Pro-Competition Interventions", which allow the CMA to "address specific competition problems arising from a firm's market power in a particular digital activity".
In other words, the CMA could have the legal power to tell Apple it must allow rival app stores on iPhone, as in the European Union.
Last year, the CMA closed an earlier, long-running investigation into Apple's app store based on powers granted by the UK's older Competition Act. At the time, the authority highlighted the potential for a speedier investigation under the newer DMCC, which would allow it to address issues "in a more timely, holistic, and flexible manner".
The CMA now expects to have reached a decision on Apple and Google's SMS status within nine months.