Section 203(a) of Title 47 of the United States Code requires communications common carriers to file tariffs with the Federal Communications Commission (FCC). Section 203(b) authorizes the FCC to “modify” any requirement of § 203. Beginning in 1979, the FCC decided to make tariff filing optional (called permissive detariffing) for all nondominant long-distance carriers. The rationale for this decision was to reduce costs on new entrants to the long-distance carrier market. The permissive detariffing applied to nondominant carriers, resellers and specialized common carriers, such as MCI Telecommunications Corp. (MCI) (defendant). AT&T, the dominant carrier, filed a complaint with the FCC challenging MCI’s failure to file tariffs. The FCC dismissed AT&T’s complaint, finding that MCI was in compliance with the FCC’s rule on permissive detariffing. AT&T petitioned for review of the rule in the Court of Appeals for the District of Columbia Circuit. The court of appeals found that the FCC did not have authority to enact a permissive detariffing policy. The FCC then released a report and order finding that the permissive detariffing policy was within its authority under the Communications Act. AT&T filed a motion with the D.C. Circuit seeking summary reversal of the FCC’s order. The D.C. Circuit granted the motion.