Yes, there are legal limits to what you may do, but your hands are not completely tied. In fact, you may be surprised at how much influence you can have.
Here are some straightforward guidelines:
From the IRS:
* Internal Revenue Service Web page containing many valuable resources on federal tax regulations pertaining to section 501(c)(3) tax-exempt organizations and political activity
* February 2006 Internal Revenue Service fact sheet providing further understanding of federal tax law for 501(c)(3) organizations, including most churches, with a special emphasis on prohibited activity