AT&T has called out two of its competitors, Sprint and T-Mobile, over their decision to offer Wi-Fi calling support on smartphones without first getting proper authorization from the Federal Communications Commission in a letter to that organization’s chairman.

According to AT&T, the FCC has been too slow in issuing a waiver that would allow the company to bypass certain requirements for hard-of-hearing users—a move that’s necessary for Wi-Fi calling to work.

Namely, AT&T is looking to offer Wi-Fi calling without support for teletypewriter, or TTY, devices, which “do not operate reliably on…Wi-Fi networks.” Because support for these types of devices is required by the FCC on all voice calling networks, AT&T can’t roll out Wi-Fi calling until they get a waiver releasing them from the requirement.

AT&T planned to roll out its Wi-Fi calling feature with the launch of iOS 9, and indeed still works for some users who were able to activate it in their area during the beta, but the service remains limited to only a handful of testers right now until the carrier can secure the proper paperwork.

T-Mobile and Sprint have both offered Wi-Fi calling without getting the needed authorization from the FCC, essentially putting AT&T at a disadvantage for playing by the rules.

AT&T isn’t trying to lock out deaf users on Wi-Fi calling, however. Instead, the carrier has plans to implement a newer system called RTT (real-time text) in early 2016. Along with the waiver, the carrier is seeking a change to FCC rules that would allow this new standard to be added as an acceptable alternative to the TTY requirement industry-wide.

The new RTT standard has the backing of employees within the FCC as well as advocacy groups for the disabled. There was also no public opposition to the request after a 45-day comment period opened by the FCC in July, three weeks after both proposals were first submitted.