A 501c3 tax exemption allows for the donations to be tax-deductable, and the donations to the church to be tax-exempt. So $100 donated provides for a $100 deduction for the contributor, and the full $100 to be used by the church.
A very flimsy line is drawn as to how much money can be spent on political, legislative agendas. With the PROP 8 campaign, the Mormons have clearly overstepped this line, and called out "what the hell you gonna do about it?"
Petition to change the 501c3 status of the Mormon church empire to 501c4. This changes tax exempt status of the donations by the contributors. Now, a $100 donation, would be like money spent at McDonald's - the contributor would receive no tax benefit from it. The Mormon church under 501c4 would have the same status of most of the PACs out there - the church would still be a non-profit, and could then legally play lobbyist.
The First Amendment does not guarantee that a church will be a 501c3. That designation is determined by the IRS based on the Mormons behavior, how much it is spending versus on how much it brought it - we don't know those numbers - Mormons are secretive about their finances.
Again, secrecy is OK, but it doesn't rate a 501c3 status.
Mormons want to legislative and run petitions to overturn same-sex marriage laws, then Mormons don't need the 501c3 status.
The first step is to guage the "need" with an online petition.
When Mormon tax-exempt status was threatened in 1978 by the Carter Administration, all of a sudden, the Mormon God said, let those blacks have priesthoods, they are after the money. So when the money is attacked, Mormons will behave.
Online Petition To Change Tax Exempt Status of Mormons