The lawsuit, which was filed on Thursday with the U.S. District Court in San Jose, Calif., alleges that Apple (AAPL) “intentionally broke” FaceTime apps running on April 16, 2014. Apple only broke, or intentionally turned off, the app on those who were running iOS 6 or earlier versions of its mobile operating system, and appears to have only affected iPhone 4 and iPhone 4S owners. The decision to turn off the app for those users, the class argues, was made so Apple could save money on charges related to calls made through the service by forcing users to upgrade to iOS 7.

Apple’s FaceTime was introduced in 2010 as a way for users to make video calls with other iOS device owners. FaceTime also works with Macs, allowing users to place calls from mobile devices or computers and hold a full video chat.

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According to the lawsuit, which was earlier obtained by Apple-tracking site AppleInsider, Apple used two methods for delivering video calls. The first was peer-to-peer technology, which directly connected one device to another during a call. Apple is also said to have employed a “relay method” in which both the caller and the recipient connect to a relay server on the Internet, and the data for the call flows through those servers to both devices.

Between 2010 and 2012, the vast majority of FaceTime traffic—the plaintiffs estimate 95%—relied upon peer-to-peer networking. However, in 2012, a jury said Apple was violating patents held by security company VirnetX (VHC) in its peer-to-peer FaceTime calls and would therefore need to switch all of the traffic to relay method to avoid infringing VirnetX’s patents.

“Upon shifting 100% of FaceTime call volume to the relay method, Apple’s relay usage soared,” the lawsuit says. “As a result, Apple began to incur multi-million dollar monthly charges for its use of Akamai’s servers.”

Akamai (AKAM), a content delivery company, was operating the relay servers.

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Then, the plaintiffs say, Apple tried to find a way around its problem. In iOS 7, the plaintiffs allege, Apple was able to revert FaceTime calls to the peer-to-peer method by using a technology that VirnetX didn’t hold a patent on. The move meant that iOS 7 users would no longer run calls over the relay servers and could save Apple boatloads of cash each month.

“Internal Apple emails eliminate any doubt that Apple intentionally broke FaceTime, and did so in order to reduce relay usage and the high costs related thereto,” the lawsuit reads.

In response, and after months of iOS 7 availability, the plaintiffs say Apple “broke” FaceTime for iOS 6 users to “force” them into running iOS 7 if they wanted to once again access FaceTime. If they stayed with iOS 6, they wouldn’t be able to access FaceTime. The lawsuit also alleges that Apple called its allegedly intentional move a “bug” that would only be fixed by updating an affected device to iOS 7.

“It was a big user of relay bandwidth,” an Apple engineer allegedly wrote in an email obtained by the plaintiffs. “We broke iOS 6, and the only way to get FaceTime working again is to upgrade to iOS 7.”

For its part, Apple hasn’t confirmed the legitimacy of the emails and has yet to respond to a Fortune request for comment on the lawsuit. The company indeed reported in a support page in 2014 that its FaceTime was suffering from a problem with a “bug” that would only be fixed with iOS 7. However, Apple has never confirmed that the bug was created by the company to get users to download iOS 7.

The class is suing Apple for unspecified damages and claims the company violated California’s competition law.