With so much attention on tech giants, it is almost possible to overlook the doings of AT&T, the once fearsome telephone monopolist. Even in an age of bigness, it is a behemoth. Its revenue, $160 billion in 2017, is four times that of Facebook. And AT&T boasts 166 million paying wireless and video subscribers in the United States.

And yet the company wants to build an even bigger empire. AT&T is seeking to acquire another giant, Time Warner, the owner of HBO, CNN, Turner Networks, the Warner Bros. studios and DC Comics, among other media properties. Their planned merger would create a union of pipes (AT&T) and content (Time Warner) that would be the largest such company in the world.

After years of approving far too many mergers — consider the airline industry — the Justice Department has challenged AT&T’s plan under antitrust laws and delivered its opening arguments against the merger in Federal District Court in Washington on Thursday. According to the department, the merger is broadly anticompetitive and would raise the costs of television for consumers across the nation by an estimated $436 million per year, or 45 cents a month per subscriber. AT&T calls that number “insubstantial” and “negligible” relative to what Americans pay for television.