By Dan Merica, CNN

Washington (CNN) – A coalition of atheist and secular organizations are coming together on Saturday to hold what is being billed at the largest gathering of atheists in history.

David Silverman, chairman of the event committee and president of the American Atheists, said the rally is aimed at uniting atheist organizations and letting the religious know that there are nonbelievers among them.

“We need to stress to the theists that we are here,” Silverman said. “Atheism is growing in all 50 states. What people don’t seem to understand is all we demand at American Atheists is equality.”

Silverman initially told CNN that the rally would draw anywhere between 10,000 and 20,000 people to the National Mall, and the National Park Service has planned for 30,000 people. With thunderstorms forecast for Saturday, however, Silverman told CNN on Thursday that he expects somewhere between 5,000 and 10,000 people.

The cost of the event is around $300,000, Silverman said, but philanthropist Todd Stiefel, Founder of the Stiefel Freethought Foundation, is supplying half the money.

CNN's Belief Blog – all the faith angles to the day's top stories

The rally has been a catalyst for protests by the Westboro Baptist Church, a group well known for its picketing of funerals of American servicemen and servicewomen. Westboro Baptist has been granted a permit for the “grassy area between 14th and 15th” streets, according to Carol Johnson, a communications officer for the National Park Service.

Though a press release for the reason rally touts 17 groups planning to protest, only the Westboro Baptist Church has applied and obtained a permit. Johnson said rally organizers have notified the Park Service of other possible protest groups, but none of those have applied for a permit.

The rally's long list of speakers and presenters runs the gamut from intellectuals to celebrities to comedians. The event is headlined by Oxford professor and author Richard Dawkins.

Dawkins, who is widely regarded as the most respected figure in atheism, is lending his voice to this event because he says freedom for atheists is “constantly under threat from people who would like to turn this country into some sort of a theocracy.”

“The Reason Rally is part of an effort to combat the attack of the theocrats,” Dawkins told CNN. “There is in this country at the moment a great revival of atheism, and the number of atheists in the country is much larger than people realize.”

Atheist organizer takes ‘movement’ to nation’s capital

At a press conference for the event, Silverman was adamant that the rally won't be the last. He didn't say whether it will be become an annual tradition, but he intends a higher profile for atheists in the future.

“The next step after the rally is all eyes on the election,” Silverman said. “We want to post hard questions to the candidates.”

Dawkins, too, related the rally to politics.

“The nonbelieving constituency has not been vocal enough, and it therefore has been politic for them to be ignored by their congressmen, by their senators,” Dawkins said.

Directing his comments at Congress, Dawkins said, “You have been neglecting them, overlooking them and riding roughshod over them as though they didn’t exist. Well, they do exist and they outnumber some of the other lobbies that you have been so assiduously sucking up to all these years.”

The America Atheists also are holding their annual convention in Bethesda, Maryland, and the Secular Coalition for America has scheduled its “Lobby Day for Reason” on Friday.

The weekend is part of a larger blitz by a coalition of atheists to “win” equality in American culture, Silverman said.

“We are the last group against whom it is politically correct to be bigoted,” he said. “That is something that needs to change and I am very confident that we will within 20 years.”