Apple is facing a $5 million class action lawsuit from a disgruntled Californian couple who say it should reimburse customers who have ran up excessive data charges due to the new Wi-Fi Assist feature launched on iOS 9.

Wi-Fi Assist, which is enabled by default, automatically switches to cellular data whenever a user's Wi-Fi connection is poor. Despite the cellular data icon appearing in a device’s status bar whenever the feature is activated, many users have reportedly not realized that they are using up their data allowance. As a result, people have allegedly been running up large bills for data usage while believing they were on their home Wi-Fi.

After William Scott Phillips and Suzanne Schmidt Phillips had to pay excess data charges on both of their iPhone 5S devices, the couple launched a class action lawsuit which alleges that Apple violated California's Unfair Competition Law, its False Advertising Law, and also accuses the company of negligent misrepresentation.

The lawsuit goes on to claim that Apple initially never even mentioned the feature, that it continues to underestimate the potential costs it could incur, and by the time the company created a support page the damage had already been done. The plaintiffs allege the total potential damages exceed $5 million.

After it received the initial complaint, Apple updated its Wi-Fi Assist support page to clarify that the feature doesn’t work when you’re data roaming, doesn’t activate with background downloading of content, and won’t work with certain third-party apps which use large amounts of data. The lawsuit argues that this is not enough. It says it “still downplays the possible data overcharges a user could incur,” and that “reasonable and average consumers use their iPhones for streaming of music, videos, and running various applications – all of which can use significant data.”

While several Android handset manufacturers have equivalent features on their smartphones, such as Samsung’s Smart Network Switch, none have faced similar lawsuits.