The state Democratic Party on Thursday accused media giant Viacom (search) of political favoritism and corporate censorship for backing out of a deal to sell billboard space for a political ad.

Party Chairwoman May Scheve Reardon (search) said the ad was set to run for a month along Interstate 70 in predominantly black sections of St. Louis and Kansas City.

The ad, featuring a black man's face against an American flag, states: "Missouri Republicans have a plan. You are not a part of it."

In a letter Wednesday, Viacom Outdoor General Manager Kyle Dorton in St. Louis told party Executive Director Jim Kottmeyer the company viewed the ad as "negative."

Viacom spokesman Carl Folta said the company saw the billboard as an "ambush ad" that used race in a divisive way.

He said the ad didn't meet Viacom's standards - the same reason given for the refusal of Viacom's CBS division to air the online liberal activist group MoveOn.org's Super Bowl ad critical of President Bush.

Scheve Reardon countered that the Democratic party ad was "fact-stating and informative."

Ann Wagner, chair of Missouri Republican Party, said "there's no place in politics for race-baiting."