PARK CITY, Utah, United States?The Mormon Church's role in helping to finance the campaign to ban same-sex marriage in California has come under scrutiny in a documentary being shown at the Sundance Film Festival.

Reed Cowan and Steven Greenstreet's "8: The Mormon Proposition" highlights the Church's role in helping to force a referendum onto ballot papers in 2008 which redefined marriage as a union between a man and a woman only.

The successful passage of the redefinition, known as Proposition 8, effectively nullified a California Supreme Court ruling that had legalized same-sex marriage in the state.

Cowan and Greenstreet's film argues that without the enormous organizational and financial support of Mormons, supporters of Proposition 8 would never have been able to mobilize enough backing for it to pass.

The documentary comes with a twist: Both Cowan and Greenstreet are both former Mormons.

"We tried to make a film that didn't attack the Church but just exposes what's been going on," Greenstreet said.

"And I hope Mormons themselves, even faithful Mormons, can see our film and look at the changes that could be made. I think the Church has lost its way."

Greenstreet said he was appalled by the Church's involvement in the California same-sex marriage debate, which he views as a betrayal of traditional Mormon values.

"I grew up Mormon, I was raised in a Mormon church. The Church sent me on a two-year mission to knock on doors and convert people to the Church and they sent me out with a message of love, compassion, understanding, charity, looking out for the poor and afflicted," Greenstreet said.

"What my Church did in California was an outrageous conflict of those ethics. And I was horrified to see the families ripped apart, their lives destroyed by a policy that came from the Church I grew up in."

Greenstreet and Cowan obtained confidential documents which reveal the Church was determined to mount a campaign against same-sex marriage even before California had ruled in favor of gay weddings.

The documents also outline how Church officials sought to fund their campaign in rural areas of California to avoid being in the front line.

"It blew my mind that those people who were supposed to be so perfect could be no different than the average Washington lobbyists," Greenstreet says.

Money for the campaign came largely from followers under pressure from Church leaders, Greenstreet said.

"The Mormon Church is a very active religion. It requires all of its members every day to be extremely proactive, proving their obedience. And that's a huge amount of pressure," he said.

According to Greenstreet, there are both heterosexuals and homosexuals within the senior ranks of the church who did not support Proposition 8.

"It's just that right now, the majority voice in the leadership of the Church wins out and it just happens to be an anti-gay voice," he said.

The documentary made its debut in Sundance as a federal trial takes place in San Francisco, where same-sex marriage supporters are seeking to have Proposition 8 overturned on the grounds that it is discriminatory and violates the US Constitution.

"I think that in the federal trial that's going on in California, people are learning more and more, through the Mormon documents, the Mormon money, that the line between church and state was bridged horribly, and that it played such a huge role in what happened with Prop 8," Greenstreet said.