WASHINGTON — A federal court on Tuesday struck down regulations that cap the soaring cost of phone calls made by prison inmates, in another rollback of Obama-era telecommunications rules.

In a 2-1 decision, the United States Court of Appeals for the District of Columbia Circuit said that while the rates charged for in-state prison phone calls could be extraordinarily high, the Federal Communications Commission exceeded its legal authority in 2015 when it created rate caps for such calls.

The decision was a blow to a 15-year effort by advocates for prisoners and their families to bring down the cost of calls from prisons, which can reach as high as $10 a minute. The calls are typically placed through private telecommunications firms.

The F.C.C. rules were challenged by telecom firms that argued against the F.C.C.’s economic calculations for price caps and told the court that the agency did not have the authority to regulate the in-state prison phone rates.