The US government filed suit Monday to block AT&T's merger with Time Warner, setting up the biggest antitrust court clash in decades over the $85 billion tieup.

The deal announced more than a year ago would merge vast content of Time Warner units like premium cable channel HBO and news channel CNN with the massive internet and pay TV delivery networks of AT&T.

"This merger would greatly harm American consumers. It would mean higher monthly television bills and fewer of the new, emerging innovative options that consumers are beginning to enjoy," said Makan Delrahim, head of the Justice Department's antitrust division.

Delrahim said AT&T with its DirecTV satellite operations and Time Warner's content "would have the incentive and ability to charge more for Time Warner's popular networks and take other actions to discourage future competitors from entering the marketplace altogether."