Antitrust lawyers were scratching their heads Wednesday over published reports that the Justice Department is insisting that AT&T sell its CNN cable network, or its DirecTV satellite television unit, if it wants to win approval to buy Time Warner.

"If that is indeed the case, to me it would seem to be at least a break in recent precedent," Kevin Arquit, co-head of the antitrust practice at Weil, Gotshal & Manges, told CNBC's "Power Lunch."

Government opposition to mega-mergers like the proposed $85.4 billion AT&T-Time Warner deal usually center on concerns that they will reduce competition and raise prices for consumers. The move would combine Time Warner's vast collection of content, from movies to cable TV networks, with AT&T's sprawling network of cable, satellite and phone subscribers.

But antitrust lawyers said that, in recent years, the remedy for those concerns in media industry mergers has been a consent decree with the acquiring company promising not to engage in anti-competitive behavior.

"The Department is committed to carrying out its duties in accordance with the laws and the facts," a Justice Department spokesman told CNBC. "Beyond that, the Department does not comment on any pending investigation."

The government's reported divestiture demands came as a surprise to investors, who sent Time Warner shares down more than 6 percent on fears the deal might not go through. AT&T's stock rose more than 1 percent.