Airlines sued to stop the rule, and the U.S. Court of Appeals for the 5th Circuit issued an injunction suggesting that the carriers were likely to prevail on the merits, and suffer irreparable harm if the rules went into effect in the meantime. DOT itself estimates the cost to comply with the new rules in the hundreds of millions.
The court heard the case, and mostly sided with DOT but still sent the rule back for reconsideration because the agency failed to follow the Administrative Procedures Act is promulgating the final rule.