Consumer group Which? is launching a £3bn legal claim against Apple ( AAPL ), alleging that the tech giant has breached competition law, in relation to its iCloud service.
Which? claimed that Apple had been "effectively locking millions of consumers into its iCloud service at rip-off prices".
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The iCloud is Apple's service that allows user to store and sync data, such as photos and files, on the cloud internet network of servers, which can be accessed across devices.
The consumer group said around 40 million Apple customers in the UK who have obtained its iCloud services over the past nine years could be entitled to a payout, if its action is successful.
What is happening and who can benefit?
Which? has filed its claim with the UK's Competition Appeal Tribunal, with the action accusing Apple of breaching UK competition law by giving its iCloud storage service preferential treatment and "trapping" customers with Apple devices into using the iCloud.
The consumer group claimed that Apple encourages users of its operating system (iOS) to sign up for iCloud storage. However, Which? said Apple then makes it difficult to use alternative cloud storage providers.
Which? highlighted that iOS users then have to pay for the iCloud service once their stored data goes over the free 5GB limit.
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The group estimated that individual consumers could be owed an average of £70, depending on how long they have been paying for its iCloud services during that nine-year period.
Annabel Hoult, CEO of Which?, said: "By bringing this claim, Which? is showing big corporations like Apple that they cannot rip off UK consumers without facing repercussions.
"Taking this legal action means we can help consumers to get the redress that they are owed, deter similar behaviour in the future and create a better, more competitive market."
This is another example of the increasing scrutiny over the dominance of major technology companies in certain sectors.
Accusations of overcharging
Which? also claimed that Apple had overcharged users for their iCloud subscriptions.
"Being 'locked-in' to this service over time could come at a significant cost in terms of price, quality and choice," the consumer group said. "With Apple being such a dominant player in the phone and tablet market, this behaviour also creates a barrier for any new cloud service providers looking to enter the market and prevents healthy competition."
Which? claimed that the resulting lack of competition had led to consumers being overcharged each year.
Which? is seeking damages for all affected Apple customers that have obtained iCloud services since 1 October 2015.
How did we get here?
The reason the action stretches back to that date is because that is when the 2015 Consumer Rights Act came into force, which included the introduction of the opt-out collective action regime.
Collective proceedings refer to legal actions brought on behalf of a group of people who have been affected by a common event or series of events.
Which? explained the collective proceedings regime had allowed it to represent large numbers of people who it believed had been harmed by anticompetitive conduct.
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The consumer group said it was urging Apple to "resolve this claim without the need for litigation by offering consumers their money back and opening up iOS to allow users a real choice for cloud services".
Which? said the next step in the process would be for it to get permission from the Competition Appeal Tribunal to act as a representative and for its claim to then proceed on a collective basis.
A spokesperson for Apple said: "Apple believes in providing our customers with choices. Our users are not required to use iCloud, and many rely on a wide range of third-party alternatives for data storage.
"In addition, we work hard to make data transfer as easy as possible – whether its to iCloud or another service. We reject any suggestion that our iCloud practices are anticompetitive and will vigorously defend against any legal claim otherwise."
Other cases
This is not the only claim to have been brought against Apple relating to competition rules.
A class-action lawsuit in the US last year reportedly claimed the tech company was overcharging its customers by monopolising cloud storage for its device users.
Meanwhile, the European Commission said in June in preliminary findings that Apple's App Store rules were in breach of the Digital Markets Act (DMA), "as they prevent app developers from freely steering consumers to alternative channels for offers and content".
In September, the EC then started proceedings to "assist" Apple in complying with its rules.
Last week, Bloomberg reported that Apple is to face the first fine under the DMA rules, citing antitrust concerns over the App Store.
Apple and Android .