(CNN) The liberal media monitoring group Media Matters for America, a longtime critic of Fox News, is mounting an advertiser pressure campaign against the conservative news network.

Media Matters is not calling for an ad boycott, per se. But it is calling out some of Fox's biggest advertisers by name.

And Fox, in turn, is denouncing the group's "intimidation" effort.

Media Matters' president Angelo Carusone, who previously led boycotts against Glenn Beck and others, said on Monday that Fox's programming "is only getting more extreme and volatile," and that's why he is taking action now.

"Fox News' never-ending focus on demonizing political opponents and front-line communities — echoing Trump and framing the struggle against these groups as an urgent matter of life or death — makes the network an increasingly bad business decision for advertisers," Carusone said

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