By Dan Merica, CNN

Washington (CNN) – When he campaigns in southern Florida on Monday, Mitt Romney will have an unwelcome traveling partner: a mobile billboard attacking his religion.

The billboard on wheels, sponsored by American Atheists, attacks the Church of Jesus Christ of Latter-day Saints for its treatment of African-Americans and gays, though the church says the attacks are inaccurate.

The billboard, which American Atheists says will follow the Romney campaign for seven days, features two messages on Mormonism: “No Blacks Allowed (until 1978)” and “No Gays Allowed (Current).”

The first line is a reference to the church’s practice of denying lay priesthood to black male members until 1978.

Though the church did not allow black male members to be ordained before that year - when the church head says he received a revelation to reverse the policy - it did allow blacks and members of all racial and ethnic groups to be church members. According to The Second Book of Nephi, a part of Mormon doctrine, “Black and white, bond and free, male and female; … all are alike unto God.”

The billboard’s second line refers to what American Atheists President David Silverman says is the religion's “intolerance” and “bigotry” when it comes to the lesbian, gay, bisexual and transgender community.

But the church denies such categorizations. It accepts gay members, though church doctrine condemning homosexuality has not changed and the church strongly opposes same-sex marriage. Some gay rights activists say the church is subtly growing friendlier toward the LGBT community, including voicing support for some gay rights.

"People are surely free to disagree with us on the facts," Dale Jones, a church spokesman, wrote in an e-mail to CNN. "This group seems not to know that there have been black members of the Church since our earliest history, and there are many faithful gay members of the Church today."

Jones continued: "We would be happy to introduce the (American Atheists president) to any of our millions of members of different ethnicity who would be happy to educate him on our racial diversity."

Silverman denies the billboard, which is costing the group $8,000, is an attack on Romney specifically. A spokeswoman for the Romney campaign said she would not comment on the sign.

“Nobody seems to be talking about the implications of having a very religious Mormon president,” Silverman said. “There are a lot of things about Mormons that people don’t know, including the fact that racism is an important part of their dogma.”

The LDS Church has largely tried to stay out of the politics surrounding the presidential campaign, even though it has received increased attention due to Romney’s candidacy. This billboard, writes Jones, is "obviously" about the "personal politics" of American Atheists.

"We have consistently kept out of the political campaign," Jones wrote. "People can see this (billboard) for what it is."

American Atheists has a long history in using billboards to call out religion and get its message out. During the political conventions in August and September, the group put up billboards attacking Mormonism and Christianity, taking aim at the faith of both presidential candidates.

This mobile billboard, however, is a departure from the standard American Atheist tactic of multiple billboards on multiple religions. According to Silverman, this is because Romney’s faith hasn’t been addressed enough in the 2012 election.

“We all understand the implications of having a Christian president. We do not understand the implications of having a Mormon president,” Silverman said. “We are not taking a position on the election, we are taking a stance on ignorance.”