Some iPhone customers with limited data plans faced unexpectedly high bills when Apple introduced the new Wi-Fi Assist feature, prompting some overcharged users to lodge a class action lawsuit against the tech company.

Wi-Fi Assist was designed to improve customers' Internet browsing experiences, automatically utilizing a mixture of Wi-Fi and cellular data to create the best connection. However, the feature also had the potential to drive up bills.

Customers with low data plans were suddenly informed they went over data quotas because of Wi-Fi Assist, CNet reports. These customers claimed that they did not know Wi-Fi Assist was enabled, and they thought they were using Wi-Fi to browse the web.

A couple, who received a costlier bill than expected because of Wi-Fi Assist, filed the class action complaint in a U.S. District Court in San Jose, California. This lawsuit was first spotted by AppleInsider.

William Scott Phillips and Suzanne Schmidt Phillips of Edgewater, Florida claimed they did not know about the Wi-Fi Assist feature. They insisted Apple should pick up the extra charges on their bill due to data overages. The couple also claimed Apple should pay the bills of other customers who experienced the same problem.

The suit alleged that together the customers are owed $5 million in overage costs.

Apple posted an online guide to Wi-Fi Assist after some customers complained about the charges.

"Because you'll stay connected to the Internet over cellular when you have a poor Wi-Fi connection, you might use more cellular data," Apple said in the guide. "For most users, this should only be a small percentage higher than previous usage."

The plaintiffs in the lawsuit said that the guide came too late for them, and they had already gone over their data quota. The couple added that they only found out about the problem when they read tweets and articles about it. 

Customers can turn off the feature by going into their settings, selecting cellular or mobile data, and scrolling down to Wi-Fi Assist.