Pressure is mounting on the Department of Justice to investigate alleged antitrust violations committed by Comcast.

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The American Cable Association (ACA), a lobbying group for midsize cable operators, sent a letter on Nov. 6, demanding an investigation citing the “substantial competitive harm” it has already provided consumers.

The letter was addressed to Makan Delrahim, assistant attorney general for the Antitrust Division, and a hawk on antitrust issues.

Under Delrahim, the DOJ is appealing the AT&T-Time Warner deal over concerns the merger will inhibit competition. Both AT&T-Time Warner and Comcast-NBCU are vertical mergers, meaning the deals marry a content producer with a content distributor.

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ACA says Comcast’s cable distribution, combined with NBC’s content, make it an even greater anti-competitive threat than AT&T-Time Warner. Comcast owns 11 local news channels and seven regional sports networks, giving the company a greater ability to squeeze regional competitors.

ACA says Comcast has already violated antitrust laws repeatedly – exerting price pressure by withholding “must-have” programming from local stations, squeezing rival cable distributors by threatening to raise prices and refusing to carry certain channels. Customers fear other services, like Hulu, will soon be gone as well.

When the DOJ and the Federal Communications Commission (FCC) approved the deal in 2011, they were concerned the merger would post a threat to competition, which is why they only approved the merger with a set of guidelines governing Comcast-NBCU.

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