On Wall Street, Time Warner fell 6.5 percent to close at $88.50, while AT&T shares jumped 1.1 percent to close at $33.44.
However, according to the United States news site Wired, it's not clear whether the DoJ could successfully block the merger.
AT&T Inc will not sell cable network CNN to win antitrust approval of its proposed $85.4 billion purchase of media company Time Warner Inc and will fight the government in court if a negotiated settlement is not reached, the wireless company's chief executive said on Thursday.
In the on-stage interview, Stephenson said that if AT&T is required to sell "some of the key franchises of the business that are the most desired for the business plan. we would move to litigation".
The president's vocal opposition to CNN and the deal will come up in any lawsuit, said Matthew Cantor, an antitrust attorney.More news: After tax crackdown, Apple found new shelter for profit
Monday, the DOJ advised the companies that it would not sign off on the merger unless they agree to divest the merged company of CNN, which the president regularly condemns as a supposed purveyor of what he calls "fake news". The White House has said Trump has not spoken to the attorney general about the matter.
This week, Delrahim and other agency officials told AT&T that the deal as it now stands raises anti-competition concerns, and that the company will need to shed some assets, perhaps either Turner or DirecTV. But many, including AT&T executives, expected the acquisition to be finalized by the end of the year, and the DOJ's pushback has all but ensured that won't be the case. As a candidate, Donald Trump vowed to block the deal because it concentrated too much "power in the hands of too few".
AT&T hopes to benefit from marrying all of Time Warner's assets to its own.
AT&T has argued against selling off either company's assets, as it believes this would undercut the rationale for the tie-up. "And likewise I have never offered to sell CNN", he said, adding that there was "absolutely no intention" that the company would sell the network. "It's hard to imagine an antitrust argument that will be compelling" from the government, he said.
In an emailed statement, the Justice Department said that it "is committed to carrying out its duties in accordance with the laws and the facts".