Vaughn E. James (Texas Tech) has posted Reaping Where They Have Not Sowed: Have American Churches Failed to Satisfy the Requirements for the Religious Tax Exemption? 43 Cath. Law. 29 (2004), on SSRN.  Here is the abstract:

This article explores whether American churches have failed to satisfy the requirements for the religious tax exemption. The article reviews the historical development of the religious tax exemption through Judeo-Christian history to post-revolutionary America as well as the current law regarding religious tax exemptions. The article reviews attempts over the last fifty years by American churches to engage in lobbying and political activities and shows that today’s churches have been engaging in ever-increasing amounts of political activity. The article discusses how the Internal Review Service has failed in its efforts to enforce laws against lobbying and political campaigning by churches and proposes a three-part solution to the problem, in effect ensuring that churches in America no longer reap where they have not sowed.