Warning of a “gross concentration of power” in the news media, Senator Bernie Sanders has sent a letter urging the Department of Justice to block a proposed merger of AT&T and Time Warner, Inc.

“This proposed merger is just the latest effort to shrink our media landscape, stifle competition and diversity of content, and provide consumers with less while charging them more,” Sanders wrote in a letter to the head of the department’s antitrust division. “This merger represents a gross concentration of power that runs counter to the public good and should be blocked.”

AT&T announced Saturday that it had agreed to an $85.4 billion acquisition of Time Warner, a move which must be approved first by federal regulators.

Consumer groups also weighed in in opposition to the merger.

“When merger authorities get the call from AT&T asking for approval of its proposed Time Warner acquisition, they should slam down the phone in disgust,” said Robert Weissman of Public Citizen “It aims to concentrate far too much market, communications and political power in one corporation, threatening to impede the free flow of information, undermine the integrity of the Internet, raise consumer prices and further corrupt our politics. This is not a proposal that can be fixed with tweaks, divestitures or conduct agreements. Antitrust authorities should reject this merger proposal out of hand.”

Sanders said that the diversity of programing would be further diminished by truncating the relationship of content and distribution.

“When one giant company owns both the content and the means of distribution, there is a clear disincentive to provide additional choices to consumers,” Sanders wrote.

Consumers have seen negative outcomes from companies who use their scale and power to raise prices in the past.

After AT&T acquired DirecTV in 2015, AT&T raised prices for DirecTV services. AT&T also exempted DirecTV streaming video from data caps on AT&T’s mobile Internet service.

“The media and telecommunications landscape is changing. It is important that public policy concerns guide these changes, so that we may preserve our democratic discourse and open competitive markets for speech and commerce,” Sanders wrote.