President Donald Trump took to Twitter to denigrate Comcast Corp. (CMCSA - Get Report) , echoing complaints about possible antitrust law violations that have been made by the American Cable Association. 

American Cable Association has big problems with Comcast. They say that Comcast routinely violates Antitrust Laws. "These guys are acting much worse, and have much more potential for damage to consumers, than anything AT&T-Time Warner would do." Charlie Gasparino

— Donald J. Trump (@realDonaldTrump) November 12, 2018

Charlie Gasparino is a Fox Business Network journalist, meaning Trump may have been watching the network, a rival of Comcast-owned CNBC, before sending the tweet. 

Last week, the American Cable Association sent a letter to the U.S. Justice Department thanking the agency for monitoring Comcast's vertical integration with video programmers and requesting a formal investigation into the company. 

"Further, Comcast-NBCU has shown a willingness to harm rivals, even while being subject to the 2011 DOJ and FCC conditions. In light of these concerns, which also have been expressed by members of Congress and a diverse array of stakeholders, the Antitrust Division should immediately open an investigation in the firm's behavior," a letter signed by ACA President and CEO Matthew M. Polka said. 

NBC News, which is also owned by Comcast, has been a frequent critic, and target, of the Trump administration, which believes that the news media isn't covering Trump fairly. 

Comcast shares were trading in the green for much of the day before Trump's tweet. The stock turned down 1%. 

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