A Federal Trade Commission lawsuit against AT&T will go forward, according to a ruling by United States District Judge Edward M. Chen. The suit contends that in July 2011, AT&T began throttling the speeds of the unlimited data plans of customers who were grandfathered into those plans after AT&T switched to tiered data plans.

The suit contends that AT&T throttled the unlimited plans not in response to cell-tower congestion but at times when AT&T’s network had ample capacity to carry the data.

AT&T doesn’t really dispute this but contends the FTC has no authority in the matter. It claims that as a “common carrier” it is exempt from the FTC’s ability to regulate commerce and address unfair or deceptive acts or practices.

The judge rejected this reasoning, writing, “When this suit was filed, AT&T’s mobile data service was not regulated as common carrier activity by the Federal Communications Commission. Once the Reclassification Order of the Federal Communications Commission (which now treats mobile data serve as common carrier activity) goes into effect, that will not deprive the FTC of any jurisdiction over past alleged misconduct as asserted in this pending action.”