For example, the Episcopal Church has reported that the retirement rate of its clergy exceeds the ordination rate by 43 percent. And last year, an article from an official publication of the Presbyterian Church wondered if full-time pastors are becoming an "endangered species."

This trend prompted the Religion News Service to report that, in the future, clergy should expect to earn their livings from "secular" jobs. Pastors who don’t want to go that route might have to ask friends and relatives for money, or perhaps serve more than one congregation.

“There is certainly a growing trend towards bi-vocational ministry in both mainline and evangelical churches,” says Kurt Fredrickson, a professor of pastoral ministry at Fuller Theological Seminary in Pasadena, California.

This trend dovetails with other recent developments that are troubling to many religious communities. Not only is church attendance in long-term decline, but financial giving by church members is at Depression-era lows. Meanwhile, seminary students are taking on ballooning debt for a career that may not exist by the time they graduate. This trend began before the Great Recession, and has only worsened since then.

Of the seminary students who graduated in 2011 with a Master of Divinity degree (the typical degree for a full-time pastor), more than 25 percent accrued more than $40,000 in educational debt, and five percent accumulated more than $80,000 in debt. Those lucky enough to get a full-time job as a pastor will join a profession whose median wage is $43,800, according to the U.S. Department of Labor.

“Many denominations are concerned about the burden of student debt and how that impacts the vocational lives of clergy,” says Sharon Miller, interim co-director of the Center for the Study of Theological Education at Auburn Theological Seminary in New York City.

Miller says some denominations are addressing the problem by covering a student's tuition in exchange for a promise to later work as a pastor in that denomination. Other denominations are helping clergy who minister in underserved areas (and who thus aren't compensated all that well) pay off their student debt—“But these efforts are quite limited in scope, as denominations are financially stressed themselves,” she says.

Sometimes evangelical pastors, especially those planting a new church in an economically disadvantaged area, intentionally choose a bi-vocational life. Fredrickson says these pastors often “sense that they will be able to serve their neighborhood better if they are engaged on a regular basis in their community.” One example of a deliberately bi-vocational church is Love Chapel Hill in North Carolina, where five co-pastors share the workload of the church and work other jobs on the side.

“We are reaching an eclectic group of people,” says Mat LeRoy, one of the five co-pastors. “We have a growing core of young families and professionals, a large collection of college and grad students from [the University of North Carolina at Chapel Hill] and a beautiful group of local homeless friends. With this type of socioeconomic diversity, bi-vocational ministry is currently a strategic necessity for a sustainable outreach.” He adds, “This is not an easy choice for us, but it is worth it to continue our mission in our community."