The Family Research Council organized the gathering in support of Atlanta's recently fired fire chief, Kelvin Cochran.
Cochran self-published the book "Who Told You That You Were Naked." The GA Voice cited two passages from the book, which refers to homosexuality as unclean, inappropriate, vile and vulgar.
When his book became public, Cochran was suspended and ultimately fired by Atlanta Mayor Kasim Reed.
The president of the Family Research Council, Tony Perkins, along with other rally organizers and supporters, delivered nearly 40,000 petitions to city hall in support of Cochran. "The naked truth is that the actions taken against the chief are designed to send a message that will silence Christians and in effect force them to check their faith at the door of public service," he said.
In a written statement, Reed said this is not about religious beliefs but "the city's nondiscrimination policy is nonnegotiable." "Neither race, nor gender, nor religion, nor creed, nor sexual orientation, nor physical ability, nor gender identity will be used to discriminate against any city of Atlanta employee."
Cochran spoke at the rally and said his religious beliefs have not created a hostile work environment and there has been no discrimination against any member of the LGBT community. "There are grave consequences for publicly expressing our faith and having the audacity to believe that sex was created for procreation and should be in the bonds of holy matrimony between a man and a woman," Cochran said.
His sentiments were echoed by other faith leaders who spoke in support of him.
"How are you going to tell me that I can't say what the Bible says everywhere?" asked Bishop Wellington Boone, president of the Fellowship of International Churches. "If the Bible says that a level of acts of behavior is vile affections, it's clearly vile affections," he said.
Cochran, a 34-year veteran of the firefighting profession, has spent the last seven years working for the Atlanta Fire and Rescue Department. He said his termination was unjust.
"All people, groups are welcomed and embraced in the city of Atlanta, except the groups that believe the scripture regarding God's purpose for sex," he said.
Reed said Cochran's comments eroded his confidence in the chief. "Every single employee under the fire chief's command deserves the certainty that he or she is a valued member of the team and that fairness and respect guide employment decisions," Reed said.
Reed also said Cochran failed to notify him about his plans to publish the book and called it an "irreconcilable lapse in judgment." Cochran said he received permission to write the book from the ethics director.
Cochran expressed his gratitude to his supporters and maintained: "One thing we should not have to sacrifice are the freedoms inherit in our great nation: free speech and freedom of religion."