Say what you will about the rabble-rousing folks at American Atheists. They're at least equal-opportunity offenders. The nonprofit organization known for its derisive and outspoken attacks on religion has taken public shots at Christianity, Islam, Judaism and pretty much every other organized faith on the planet.

But did the group cross the line when it tried to mock Mormonism at the site of the upcoming Republican National Convention? Some sales executives in Tampa, Fla., think it did, at least according to American Atheists President David Silverman.

"We were turned away by local bosses at three different companies," Silverman said in a phone interview. "They didn't like that we challenged Mormonism or 'attacked' it, if you want to use that word."

Silverman would not say which companies refused the ad, as the organization still does business with them. But he said the decisions were made at the local level and did not necessarily reflect specific company-wide polices about offensive ads. He said that while individual sales reps would have been willing to rent the billboard space, their efforts were blocked by higher-ups. "The reps will sell anything," he added. "It's the decision makers, not the reps. The local bosses are deciding who gets to speak and what they get to say."

As was reported on Tuesday, the billboard in question features a man floating in space next to the headline "God Is a Space Alien." (According to Mormon scripture, the throne of the Almighty is located near a star called Kolob.) The ad goes on to say, "Baptizes Dead People; Big Money, Big Bigotry." The billboard is going up this week in Charlotte, N.C., the site of September's Democratic National Convention. However, Silverman said no one in the Tampa area would rent the atheists billboard space.

According to the Outdoor Advertising Association of America, or OAAA, advertising companies do sometimes use individual discretion to refuse ads that might be deemed offensive in certain communities. In its Code of Industry Principles, the OAAA supports the right of companies to flat-out reject ads that are "misleading, offensive or otherwise incompatible with individual community standards." Where specifics are concerned, however, the OAAA mostly takes aim at curbing obscenity and keeping billboards kid-friendly. The organization was not available to comment on the anti-Mormon ad, but according to its code, it advocates the use of outdoor advertising for "political, editorial, public service and other noncommercial messages."

Silverman, meanwhile, said the rejection was less about community standards and more about timing. He said it's no coincidence that the ad was refused in the same city where Mitt Romney is expected to receive the Republican nomination later this month.

"This wouldn't have been an issue a few years ago," he said. "What's going on here is an attempt to make Mormonism mainstream. Obviously, if we come out with a billboard exposing it for the ridiculousness that it is, it's going to make things difficult for folks down there."

Silverman said he believes the Tampa exes would have agreed to a compromise, but aside from being "flexible with the wording," he said he was not willing to dilute or tone down the ad. "This is what the religion says," he added. "God is a space alien."

This isn't the first time American Atheists has gotten into a billboard dust-up with a local community. In May, the group was rejected by a Brooklyn building owner when it tried to erect a billboard that called the Jewish faith a "myth." The building was in a neighborhood with a large Jewish population.

American Atheists often uses loaded language in its advertisements. One of the group's new billboards calls the Christian god "savage" and Jesus a "useless savior." While Silverman is aware that such wording will turn off people of faith, he said his group is more concerned with empowering the faithless. If atheism were more socially acceptable, he believes, more people would be willing to come forward and affirm themselves as nonbelievers.

"We're never going to reach the devoutly religious, and nor do we care," he said. "Atheists aren't trying to convert the religious. We're trying to turn closeted atheists into outed atheists.