Apple has been hit with a $5 million class action from 4s iPhone owners seeking damages for deceptive trade practices and false advertising.
The lawsuit comes after reports that the older model iPhone's functions are disrupted after users upgrade to iOS 9 software.
What you need to know about Apple's iOS 9
Apple has made some small but marked improvements to its mobile operating system.
More than 100 people have joined the class action filed on 29 December, claiming the iOS9 rendered their 4s iPhones essentially unusable, according to documents published on AppleInsider.
Planned obsolescence is at the heart of the lawsuit, with plaintiffs claiming the upgrade "interfered with the normal usage of the device", including touchscreen responsiveness, freezes and crashes.
The lawsuit goes further, asserting that the tech giant and engineers at Cupertino were aware of the deleterious effects the iOS 9 upgrade on the 4s models through internal testing, or "other means", yet proceeded with the upgrade regardless.
The class action is also critical of Apple's advertising campaign, claiming it misleads consumers by suggesting the upgrade would increase the performance and battery life of the iPhones.
The final insult: a number of the plaintiffs claim they were forced to purchase new iPhones, arguing that the iOS "ecosystem" meant users were loathed to switch to a competitor.
iOS9 copped heavy criticism when it launched in September for slowing down even the latest generation iPhones.
A significant number of Apple customers complained that their mobile devices crashed after attempting to upgrade to the new upgrade, the latest in a line of launch glitches for the tech giant.
Twitter and other social media were awash with disgruntled customers reporting two distinct faults, with one appearing to be linked specifically to older models of Apple iPhones and iPads.
iOS9 claimed to have, for the most part, fixed the problem, 9to5Mac reported.