Sen. Richard Durbin, D-Ill., warned against the proposed merger of Sinclair Broadcast Group and Tribune Media, writing in a Crain's editorial Monday the proposed deal "threatens to do permanent damage to the American tradition of local broadcasting and will take a wrecking ball to the pillars of objectivism and diversity in local broadcasting."

The proposed merger would put the conservative-leaning Sinclair in more than 70 percent of American homes, but Durbin said his concerns are not with ideology, but diversity of viewpoints, as FCC rules currently encourage.

Those rules limit the total number of broadcast outlets a single company can own nationwide as well as the number of stations one company can own in a single market.

Softening those rules, as Trump-appointed FCC Chairman Ajit Pai, has done, would erode the public's trust in local broadcasters and "fundamentally change the nature of broadcasting in America," Durbin said.

"What was Pai's motivation for putting this loophole back in place?" Durbin asked. "I'll just note one coincidence: The loophole was reinstated in April and Sinclair announced its acquisition of Tribune in May."

Tribune-owned WGN in Chicago would be among the stations falling under the Sinclair umbrella should the merger take place, putting Sinclair's conservative editorials and programming into more than 80 million homes nationwide that receive the superstation via cable and satellite.

"This is not the broadcast media Americans deserve," Durbin said. "It is my hope the FCC will not take any further actions to relax its media ownership limits without an honest public review of the state of the broadcast marketplace today."

Sinclair has said it is willing to sell off some of the stations to meet the FCC's limits.