A group led by privacy activist Max Schrems filed complaints this morning with German and Spanish data protection authorities over Apple's online tracking tool, saying it breached European law by allowing iPhones to store users' data without their consent.
It is the first such major action against the U.S. technology group related to European Union privacy rules.
Noyb, the digital rights group run by Schrems, has successfully fought two landmark trials over privacy against Facebook.
Apple said it was not immediately in a position to comment.
The Californian tech giant has previously said it provides users with a superior level of privacy protection. It had announced it would further tighten its rules with the launch of its iOS 14 operating system this autumn but in September said it would delay the plan until early next year.
Noyb's complaints were brought against Apple's use of a tracking code that is automatically generated on every iPhone when set up, the so-called Identifier for Advertisers (IDFA).
The code, stored on the device, allows Apple and third parties to track a user's online behaviour and consumption preferences - vital for the likes of Facebook to be able to send targeted ads that will interest the user.
"Apple places codes that are comparable to a cookie in its phones without any consent by the user. This is a clear breach of European Union privacy laws," said Noyb lawyer Stefano Rossetti.