They've tried noisy protests, consumer boycotts, and the odd act of minor terrorism. Now supporters of gay marriage have unveiled a new weapon in their war against the Mormon Church: satire.

The creators of the cartoon South Park, Trey Parker and Matt Stone, are planning to stage a Broadway musical based on the lives and (many) loves of typical members of the Church of the Latter Day Saints.

It will be co-written by the composer Robert Lopez, who wrote Avenue Q, the award-winning musical which sends-up another all-American institution, Sesame Street.

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Cheyenne Jackson, an openly-gay Broadway star who appeared in the film United 93, said this week that he has agreed to play the lead role, a Mormon missionary, in the show, which is currently being work-shopped and is slated to open in 2009.

"It's hilarious: very acerbic and biting," he told the New York Post. "It offends everybody, but does what South Park does best, which is [that] by the end it comes around and has something great to say."

Though he didn't reveal details of the plot, or say who else would be starring in the show, Jackson added that it has the working title of Mormon Musical. "I play the main missionary, Elder something," he said.

News of the potentially-controversial project comes at a tough time for the Mormon Church, which is fighting a propaganda war over its role in passing Proposition 8, the ballot measure that outlawed same-sex weddings in California this month.

The Church joined a coalition of religious groups supporting the Proposition, and members donated tens of millions of dollars to finance a raft of often-misleading attack adverts, which helped persuade 52.5 percent of the State's electorate to support the measure.

A series of noisy protests have since targeted Mormon temples, and church property across America has been vandalised. On Friday, two temples in Los Angeles and Salt Lake City, the home of Mormonism, were at the centre of an Anthrax scare, after being sent envelopes containing white powder.

Activists in Hollywood, the centre of LA's gay community, have urged their supporters in the world of show-business to back a consumer boycott of companies that helped finance the gay marriage ban.

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The Sundance Film Festival, which begins in January, is particularly threatened by the boycott, since it takes place in the Utah ski resort of Park City, just a short drive from Salt Lake City.

Actors and producers have been urged to pull their films from a Cinemark Theatres complex providing four screening rooms to the Festical. The company's CEO, Alan Stock, contributed $9,999 to the Yes on 8 campaign.

Campaigners have already forced the resignation of Scott Eckern, artistic director of the Sacramento Musical Theater, who donated $1,000, and are calling for Rich Raddon, director of the Los Angeles Film Festival and another donor, to also be fired.

Whatever Mormon Musical's eventual contents, the creators of South Park certainly have form for offending religious minorities. One of their cast members, the late Isaac Hayes, quit the show in 2006 over what he described as its "bigoted" portrayal of Scientology.

Their 1999 film Bigger, Longer and UnCut attacked both Saddam Hussein and the people of Canada, and sailed close to the wind dealing with the issue of race. However it was shortlisted for an Oscar for its soundtrack.

Jackson is active within the gay rights community. His comments regarding the project were made an awards show organised by the gay magazine Out. "As frustrating as Prop 8 has been, we have to look back at the last 60 years and see how far we've come," he added.