Comcast Corp. and Time Warner Cable Inc. fired back at critics of their proposed $45 billion merger, accusing them of engaging in "extortion" to extract business concessions and win their support for the deal.

In comments filed with the Federal Communications Commission late Tuesday night, the companies took shots at streaming-video juggernaut Netflix Inc., cable channel-owner Discovery Communications Inc., and Glenn Beck's The Blaze, among others.

Comcast said various parties made requests after the transaction was announced with an "implicit offer" to support the deal—or at least not actively oppose it—if their demands were met. The demands included asking Comcast to share access to its advanced advertising technology, carry yet-to-be-launched TV networks, pay higher carriage fees for channels and allow interconnection of Web traffic without charge, Comcast said.

"The Commission should forcefully reject these extortionate, anti-consumer efforts, which clearly have nothing to do with the public Internet," Comcast said in its filing. On a call with reporters, Comcast Executive Vice President David Cohen clarified that despite the tough language "we are absolutely not accusing anyone of criminal activity in connection with the transaction."

Comcast singled out Netflix for trying to gain undue business leverage. It cited an email from Netflix CEO Reed Hastings to Comcast executives in which he praised a paid interconnection deal the companies struck early this year to improve Netflix streaming quality for Comcast subscribers, saying the arrangement "worked well for both of us for the long term." Comcast noted Mr. Hastings later took a markedly different stance in the merger proceedings and has since opposed the Comcast-TWC deal.