If you are interested in an more in-depth discussion of lobbying activities by public charities -- please check out an article I wrote that was recently published in the Minnesota State Bar Association's Tax Section News. The article is titled "Advising Public Charity Boards on Lobbying Activities." It is generally geared towards the advisors of nonprofits, but would also serve as a good resource for discussion points for organizations that are engaging in lobbying. The full article can be accessed either through my biography page, or by clicking on the above link.
Enjoy, and please forgive me for tooting my own horn!