Scores of evangelical Christians gathered this week for their regular Wednesday night prayer service at the River of Life Christian Church’s sprawling complex in Santa Clara, closing their eyes and opening their palms skyward as they rocked back and forth to soaring hymns.

The 10-acre lot just off the Bayshore Freeway where they prayed is the home base of one of the largest Chinese Christian churches in North America. River of Life has more than 2,400 local members and 10,000 more worldwide  up from 70 in 1995, said its pastor, Tong Liu. Waves of immigrants from Taiwan, Hong Kong and mainland China have filled its pews, while transforming cities like Santa Clara and Cupertino.

The increase in conservative evangelical churches in Chinese immigrant communities has had reverberations well beyond the liberal confines of Silicon Valley and the Bay Area. And no political issue has transfixed this group’s attention like same-sex marriage. It is no coincidence that Cupertino, where census estimates show that one person in four is Chinese (up from one person in 30 three decades ago), was also the site of one of the biggest Bay Area rallies supporting Proposition 8, the ballot measure that banned same-sex marriage in 2008.

But this month the little-noticed but burgeoning world of evangelical Chinese Christianity in the Bay Area has become the backdrop for crucial arguments in the federal trial in San Francisco challenging the constitutionality of the ban on gay marriage.