Ah, Bobert, the 501(c)'s include (I assume) the 501(c)3's? Like the American Library Association and Harvard and the Sierra Club and the NAACP? 501(c)6's, like the Customers of Dynix, Inc. (a library automation system users' group) and the National Quilting Association and other "affinity" groups?

All of these are required to file annual reports with IRS or lose their tax-exempt status. NONE of them can contribute to candidates or lobby legislators on any level -- which is why they set up seperate groups to do this, and these fall under a different set of laws.