When you say the word "nonprofit" most people think of public charities, also called Section 501(c)(3) organizations. There's good reason for this: there are over 1.2 million public charities in the United States. However, public charities are only one of 29 types of nonprofit organizations recognized by the tax code. Next in popularity to public charities are social welfare organizations--at last count there were over 82,000.
Social welfare organizations are created under Section 501(c)(4) of the Internal Revenue Code and are often referred to as 501(c)(4) organizations. Their primary purpose is to in some way promote the common good and general welfare of the community—for example, "by bringing about civic betterments and social improvements."
There are two big differences between public charities and 501(c)(4) social welfare organizations:
One big difference between 501(c)(3) public charities and 501(c)(4) social welfare organizations is that contributions to 501(c)(3)s can be tax deductible, while contributions to 501(c)(4)s are never deductible. However, since both are nonprofits, they need not pay income tax on their income unless they are engaged in some type of business activity unrelated to their mission.
Because donations to them are never tax deductible, Section 501(c)(4) organizations are not required to get IRS approval of their tax-exempt status. However, many seek IRS approval anyway. It helps to show that they are a legitimate organization. Indeed, the IRS says that the number of 501(c)(4)s seeking IRS approval has doubled in recent years.
Because contributions to Section 501(c)(3) organizations are deductible, they may only play a limited nonpartisan role in elections. They are flatly prohibited from intervening in political campaigns in any manner whatsoever, whether by endorsing or opposing candidates for public office, mobilizing supporters to help elect or defeat candidates, or giving money to political campaigns or political parties. This prohibition applies to all political campaigns for elective office, including those at the federal, state, and local level, and even includes elections in foreign countries. A public charity that violates these rules can lose its tax exemption. (For more information, see Limits on Political Campaigning for 501(c)(3) Nonprofits.)
In contrast, because contributions to a social welfare organization are not tax deductible, a social welfare organization may engage in unlimited lobbying as long as it advances its tax-exempt social welfare purpose. For example, a social welfare organization created to help improve public health could spend its money lobbying Congress to provide more funding for public health. But it could not lobby Congress to increase the budget for space exploration.
Social welfare organizations can also engage in extensive political campaign activity. As a result of the United States Supreme Court's controversial decision in Citizens United v. FEC, 501(c)(4) nonprofits can spend their money (both voluntary contributions and general treasury funds) to support or oppose candidates for the U.S. House, U.S. Senate, and President. However, there are still some important limitations on 501(c)(4) political activities:
In addition, social welfare organizations that spend money on political activity can become subject to a special tax on the lesser of the organization's net investment income or the total amount spent on political activity. The applicable amount is taxed at the corporate tax rate—21%. Organizations that don't have investment income need not worry about this tax. (See IRC Sec. 527.)