When the Federal Trade Commission (FTC) sued AT&T in October 2014, the commission alleged that AT&T failed to disclose to its customers, who were under the carrier's unlimited data service, that their network speeds could be throttled.

This move, the FTC says, resulted in the slowing down of the customers' data speeds by up to 90 percent. The commission alleged that there were at least 3.5 million mobile phone customers who were affected by AT&T's move to reduce their transmission speed.

Now, however, AT&T claims that the FTC never had the jurisdiction to file the lawsuit in the first place. The carrier company supported this claim by reiterating that Section 5 of the FTC Act, which provides for the exemption of common carriers, does not cover telephonic voice services.

AT&T is using the common carrier status of mobile voice in order to avoid the FTC's regulation. The carrier also expressed that the FTC lawsuit deals with issues that are identical to the issues being investigated by the Federal Communications Commission (FCC).

In its filing at the San Francisco federal court, AT&T said that mobile data services are under the FCC's regulation and that the FTC does not have the same authority to file the lawsuit.

"It is the FCC, not the FTC, that regulates network management practices," said Mark Siegal, AT&T spokesman.

The FTC's complaint against AT&T is based on the carrier's MBR program. The complaint cited two counts that fall under Section 5 of the FTC Act. The first count deals with the "Unfair Mobile Data Throttling Program."

"Notwithstanding mobile data contracts that were advertised as providing access to unlimited mobile data, AT&T imposed significant data speed restriction on customers who used more than a fixed amount of data in a given billing cycle," the FTC asserted.

The second count deals with the "Deceptive Failure to Disclose Mobile Data Throttling Program."

"[AT&T] has represented, directly or indirectly, expressly or by implication, that the amount of data that unlimited data customers could access in any billing period would not be limited and that since August 2011, Defendant has failed to disclose, or has failed to disclose adequately, that it imposes significant and material data speed restrictions on unlimited mobile data plan customers who use more than a fixed amount of data in a given billing cycle," the document stated.

While the FTC lawsuit addresses AT&T's data service, which is not a common carrier product, the commission maintains that AT&T's voice service places everything within the scope of the common carrier status.