Three consumer advocacy groups are claiming wireless giant AT&T (NYSE: T) is violating FCC rules by restricting access to Apple's popular FaceTime technology, which allows users to video chat with one another, according to a Reuters report today.

AT&T will only allow those paying for the most expensive data plans to use the application on the company's cellular network, according to the report. Customers will still be able to use FaceTime on Wi-Fi networks free of charge, though connections will have a smaller coverage range.

In contrast to AT&T's restrictive policy, rival Verizon Communications, the largest domestic mobile service provider, will allow all data customers to use FaceTime, according to Reuters.

Click here to open a PDF version of the short letter the consumer groups -- Free Press, Public Knowledge, and the New America Foundation's Open Technology Institute -- sent to AT&T. The organizations said they plan to file a formal complaint with the Federal Communications Commission. Said Public Knowledge in a press release: "AT&T's subscribers shouldn't have to pay AT&T to use applications developed by Apple or any other developer. Subscribers pay for their data connections, and that's enough."