Six months after failing to block AT&T’s merger with Time Warner, the Justice Department urged a Washington federal appeals court Thursday to undo the multibillion-dollar merger deal, arguing that the combination creates a telecom giant with near-unbridled bargaining power.

The blockbuster hearing drew a close-to-capacity crowd to the U.S. Court of Appeals for the D.C. Circuit, where a three-judge panel heard arguments in what is widely considered the most significant antitrust case in decades. The panel—including Judges Robert Wilkins, Judith Rogers and David Sentelle—questioned four lawyers for two hours, allowing the advocates to speak well beyond their allotted time. As Sentelle said early on in the hearing, “We’re not very good at obeying the clock.”