The department said the merger would reduce competition and lead to higher consumer prices. AT&T vows to fight the move, calling it a radical departure from US competition practice.
AT&T chief executive Randall Stephenson said he thought the acquisition had been on a good path “until recently”.
Assistant attorney general Makan Delrahim of the Department of Justice’s antitrust division, said It would mean higher monthly television bills and fewer of the new, emerging innovative options that consumers are beginning to enjoy.
He also asserts that the combination would hurt the emergence of new online television options and give AT&T the power to force rival pay TV companies to pay “hundreds of millions of dollars more” for Time Warner content.
During his presidential campaign last October, Mr Trump said that the deal would not be approved “in my administration because it’s too much concentration of power in the hands of too few”.
AT&T called Monday’s lawsuit “a radical and inexplicable departure from decades of antitrust precedent”.
The company’s general counsel, David McAtee, said: “Vertical mergers like this one are routinely approved because they benefit consumers without removing any competitor from the market. We see no legitimate reason for our merger to be treated differently.”