The Department of Justice officially filed for an appeal of a judge’s ruling that allowed AT&T Inc. T, +1.13% to acquire Time Warner Inc. TWX, -28.57% on Thursday, setting up yet another potential court showdown for the $85.4 billion merger. In one of the largest U.S. antitrust cases in decades, U.S. District Judge Richard Leon ruled last month that the merger could go on despite the government’s resistance. The feds did not seek a stay that would have prevented the merger from taking place, and AT&T and Time Warner closed the deal directly after Leon’s ruling. AT&T stock fell 1.4% in late trading after closing with a 1.1% gain at $32.23, and has declined 17.1% this year as the S&P 500 index SPX, +0.87% has gained 3.8%.