Google's mobile telecom service Project Fi is billing customers for internet data delivered over home and public Wi-Fi networks, according to a lawsuit filed in the US on Monday.

The claim, submitted to a San Jose district court in northern California, alleged that Google is charging Project Fi subscribers for data it doesn't actually deliver.

Project Fi is a mobile virtual network operated by Google that aggregates service from different mobile carriers, specifically Sprint, T-Mobile USA, and US Cellular in America. In theory, Google bills customers $20 per month plus $10/GB of data sent over cellular networks, then compensates whichever mobile carrier's network was involved as appropriate.

According to the complaint, filed on behalf of plaintiff Gordon Beecher and seeking certification as a class action, Google tracks all data flowing through subscriber devices rather than just data traversing mobile network cell towers.

"This means that Google takes credit, and bills customers, for data delivered over the customers' home networks and public Wi-Fi connections that are available to the customer independent of Google and its mobile data partners," the complaint claimed.

"Google bills users for data obtained through alternate connections even if Google is not providing access to that data service and in many cases the customers are paying the third parties who actually provide the service."

Google's Project Fi stated explicitly that customers "are not charged for the data [they] use when connected to open or home Wi-Fi."

The complaint describes how Beecher was supposedly billed for data Google did not provide, resulting in overcharges of more than $200 for his first three months on Project Fi.

It further states that others have reported similar billing errors, citing posts on Reddit and the Project Fi Help Forum.

The lawsuit charges Google with unfair business practices and false advertising in violation of California law, as well as breach of contract.

The Register asked Google for comment, but has not heard back. ®