A Washington federal appeals court on Tuesday upheld AT&T’s planned takeover of Time Warner, another setback for U.S. Justice Department antitrust enforcers who lost their bid to block the multibillion-dollar deal after claiming it would give the newly combined company almost unbridled bargaining power.

The ruling from the U.S. Court of Appeals for the D.C. Circuit came in what observers considered one of the most consequential merger cases in Washington in decades. Indeed, the Justice Department’s push to block AT&T’s proposed acquisition of Time Warner was closely watched because it involved a rare challenge to a so-called vertical merger, a deal involving companies that are not direct competitors.