Federal tax law defines different kinds of nonprofits. Most must file a Form 990 with the IRS. These forms are public information, and you may find them at sites such as http://www.guidestar.org/.
- 501 (c)(3) organizations include charitable, religious and educational groups. They pay no taxes on income, and contributions are tax deductible. To keep this status, these groups may not support or oppose candidates for public office. Nevertheless, they may take part in a limited amount of legislative lobbying. The Berry chapter in Cigler & Loomis mentions the 501(h) test.
- 501 (c)(4) organizations generally pay no taxes on income but contributions are not deductible. These "social welfare organizations" may conduct unlimited lobbying and may do partisan campaign work, but only as a secondary activity.
- A 527 political committee pays no tax on operating income, but does pay tax on investment income. Donations are not tax deductible. Its main purpose is to influence the selection of candidates for public office. Certain kinds of 527 groups do not have to file Form 990. See here for a list of exceptions.
The IRS sums up these categories and others in a handy table.
Also consider interest-group conglomerates that may include more than one of the above types as well as a political action committee. NOW is a good example.
Another is the National Rifle Association, a 501(c)(4). It also has:
- The NRA Institute for Legislative Action, a 501(c)(4);
- The NRA Political Victory Fund), a PAC;
- The NRA Foundation, a 501(c)(3).
Though Americans still favor certain firearm restrictions, NRA is happy with recent trends in public opinion.