(FORTUNE Small Business) – Perhaps Joe Mohen should have predicted that his company would put him at odds with Southern Baptists and Mormons. But when he came up with the idea behind ParishPay-a service that allows parishioners to tithe by credit card-it hardly seemed offensive.

"I paid the phone, the cable, and the electricity by direct deposit," he says. "Why not the church?"

John Wilkerson, vice president of finance for the Southern Baptist Convention, has an answer. "Bringing your offertory and putting it in the plate is an important act of obedience," he says. "This takes the heart out of it."

"I can't imagine we'd ever do this," agrees Michael Purdy, a spokesperson for the Church of Latter-Day Saints.

Happily for ParishPay, not all churches object. Just two years old, the New York City company already boasts clients like the Archdiocese of Chicago and the Greek Orthodox Church of America. As for his critics, Mohen says they're old-fashioned.

"It's a new era, you know," he says. "People are rushed."

Still, without Mormons or Southern Baptists-two of the most generous groups of churchgoers in America-Mohen is looking for other ways to dig deeper into Catholic customers' coffers. "We're rolling out products for funerals and Catholic schools. Whole dioceses are signing up," he says happily. --NINA SOVICH