UK consumer rights group Which? launched a near £3-billion ($3.8-billion) legal claim against Apple on Thursday, saying the US tech giant locked millions of customers into its cloud storage service.
Which? said in a statement that Apple breached UK competition law by giving its iCloud storage service "preferential treatment" and therefore "trapping" customers with Apple devices into using it to store photos, videos and other data.
It claims that Apple made it difficult for users to use alternative providers, and used its market dominance to charge "rip off" prices.
Around 40 million Apple customers in the UK who have used iCloud over the past nine years could be entitled to a payout if the claim is successful, the consumer rights group said.
"We believe Apple customers are owed nearly £3 billion as a result of the tech giant forcing its iCloud services on customers and cutting off competition from rival services," said Which? chief executive Anabel Hoult.
"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," Hoult added.
Apple hit back in a separate statement.
"We reject any suggestion that our iCloud practices are anti-competitive and will vigorously defend against any legal claim," the company said.