Two-dozen conservative activists and media personalities on Tuesday urged members of their respective groups to switch off the "biased news media," claiming in an open letter that establishment media are "out of control with a deliberate and unmistakable leftist agenda."

Though these groups frequently complain about a left-leaning media bias, they claimed in the letter that the political slant this cycle is unprecedented.

"In the quarter century since the Media Research Center was established to document liberal media bias, there has never been a more brazen and complete attempt by the liberal so-called 'news' media to decide the outcome of an election," wrote Brent Bozell, president of the Media Research Center, and other conservative leaders.

They ticked off a litany of grievances against the news media, saying they've been "shamefully smearing" Mitt Romney over the course of the election.

Among their charges were that the media have painted conservative ideas as "extreme;" downplayed the "horrendous economic conditions" in the country; focused more on shortcomings in Romney's business background than in Obama's record as president; been "pouncing" on missteps by conservatives while "suppressing" gaffes by Vice President Biden; and been "deliberately covering up embarrassing government failures and scandals, including the Solyndra debacle, Fast & Furious, and national security leaks."

According to NewsBusters, part of MRC, the letter was directed at the heads of ABC News, NBC News, CBS News and CNN.

"We the undersigned -- representing millions of Americans from our respective organizations -- are now publicly urging our members to seek out alternative sources of political news in order to make an intelligent, well-informed decision on November 6," they wrote.

Network representatives have not yet responded to a request for comment.