(San Francisco, California) Hundreds of pastors have called on their congregations to fast and pray for passage of a ballot measure in November that would put an end to gay marriage in California.

The collective act of piety, starting Wednesday and culminating three days before the election in a revival for as many as 100,000 people at the San Diego Chargers’ stadium, comes as church leaders across California put people, money and powerful words behind Proposition 8.

Some pastors around the state and nation are encouraging their flocks to forgo solid food for up to 40 days in the biblical tradition.

Jim Garlow, the pastor of the evangelical Skyline Church in San Diego County, said he expects up to 100 young adults to spend five-plus weeks on his campus, subsisting on soup, juice and the promise of societal salvation.

“This is not political to us. We see it as very spiritual,” said Garlow, a leader of an interfaith coalition that has held monthly teleconferences, shared sermons and solicited donations for the ballot measure.

Alarmed by a California Supreme Court decision that legalized same-sex marriage, churches of many faiths have banded together in support of a measure that would amend the state constitution to define marriage as a union between a man and a woman. They have become the single largest force behind the measure, recruiting volunteers, raising money, registering voters, manning phone banks and distributing campaign literature.

Under federal law, religious organizations cannot endorse political candidates but are free to campaign on social issues without endangering their tax-exempt status.

Along with evangelical Christian groups such as Focus on the Family and Family Research Council, the leaders of Roman Catholic, Mormon, Southern Baptist, Orthodox Jewish and Seventh-Day Adventist congregations have endorsed the measure and urged the faithful to give.

The Knights of Columbus have given nearly $1.3 million, making the Catholic fraternal organization the largest single contributor to Yes on 8. Donations from individual Mormons account for more than $6.4 million of about $17.3 million raised so far, according to Mormonsfor8.com, a Web site set up by a church member.

Religious leaders have addressed the issue from the pulpit, in Sunday schools and Bible study meetings, and through telephone calls, letters and visits to parishioners.

The California Conference of Catholic Bishops has given the state’s 1,600 parishes Sunday bulletin inserts about Proposition 8, and every diocese is holding workshops in English and Spanish.

“This Supreme Court decision was a huge wake-up call for Catholics. It was shocking,” said Bill May of San Francisco, leader of Catholics for Protect Marriage. “The sense is that this is the last chance to restore the definition of marriage, and if unsuccessful, it is going to have serious ramifications for California and across the country.”

Mormon congregations in California are taking marching orders straight from Salt Lake City. A June 29 letter in which the Mormon president asked members to lend support to the proposed amendment has been read repeatedly at church services, along with a 1995 church proclamation that warns: “The disintegration of the family will bring … the calamities foretold by ancient and modern prophets.”

Thousands of same-sex couples have tied the knot in California in the three months since the nation’s most populous state legalized gay marriage. Massachusetts is the only other state to allow gays to wed.

Liberal congregations also have entered the Proposition 8 debate, though not as vigorously as their conservative brethren.

A coalition of religious leaders called California Faith for Equality has been working to persuade people of faith to oppose the ballot measure on spiritual and social justice grounds. California’s Episcopal bishops also have come out against the measure, which a Field Poll reported last week was opposed by 55 percent of likely voters.

“Everybody understands that Jesus, in his own culture, was notorious and persecuted for consorting with outcasts,” said the Rev. Peter Laarman, a United Church of Christ minister who opposes the gay marriage ban. “When Jesus said all are welcome at the table, I think he really meant all.”