Faced with tight budgets and in search of new sources of revenue, municipalities increasingly have been eyeing the tax-exempt status of nonprofits. Legislators say that universities' record-high endowments and the corporate-like structure of nonprofit hospitals is making it harder and harder to swallow giving these institutions a tax break.

While many of the legislative attempts to start taxing nonprofits have failed, recent legal challenges have proved more promising. If the trend continues, it could present a financial problem for nonprofits and a financial boost for governments. So far, the focus of both legislation and legal action has been on hospitals and higher education institutions, but some worry they could spill over to smaller nonprofits and charities.

The dollars at stake are significant. According to a 2009 study by the Congressional Research Service, property tax exemption is worth $17 to $32 billion nationwide.

Also driving these challenges is the issue of tax fairness. Many nonprofits fork over an annual PILOT, or Payment In Lieu of Taxes, to help offset the governments' loss of revenue. But residents in the vicinity of hospitals or universities often feel that they still end up paying higher taxes to compensate for the revenue lost to nonprofits' exemptions.