Shares of Comcast slipped Monday after President Donald Trump alleged in a tweet the company "routinely violates antitrust laws."
The stock lost just under 1 percent by the end of trading Monday, amid overall market declines.
"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," Trump tweeted Monday.
Trump's tweet follows a call earlier Monday by the American Cable Association for the Department of Justice to investigate Comcast. Gasparino, who Trump quotes in his tweet, is a reporter with the Fox Business Network.
The ACA claims Comcast owns "significant must-have local programming," allowing the company to raise prices and harm consumers. The ACA cites a recently closed merger between AT&T and Time Warner — which the Trump administration is still appealing — and claims Comcast's market power is a great threat than AT&T-Time Warner.
"We believe that ACA's letter is without merit and constitutes an inappropriate attempt to gain leverage in the commercial marketplace," Comcast said in a statement to CNBC.
Trump has previously tweeted about antitrust action against social media companies. Recently fired Attorney General Jeff Sessions held a meeting with state officials in September to review big tech and antitrust concerns.
Disclosure: Comcast owns CNBC's parent company NBCUniversal.