The Mormon Church has instructed its members to donate to proposition 8 to ban same-sex marriage in California. Nearly half the money (20 million dollars) came in from Mormon Church members predominantly from Utah.
According to IRS Law:
"Section 501(c)(3) describes corporations, and any community chest, fund, or foundation, organized and operated exclusively for religious, charitable, scientific, testing for public safety, literacy, or educational purposes, or to foster national or international amateur sports competition (but only if no part of its activities involve the provision of athletic facilities or equipment), or for the prevention of cruelty to children or animals, no part of the net earnings of which inures to the benefit of any private shareholder or individual, no substantial part of the activities of which is carrying on propaganda, or otherwise attempting, to influence legislation (except as otherwise provided in section (h)), and which does not participate in, or intervene in (including the publishing or distribution of statements), any political campaign on behalf of (or in opposition to) any candidate for public office."
Sign the petition asking the IRS to revoke the Mormon Church's Tax Exempt status.
You can also visit Revoke LDS Church 501(c)(3) status to learn how to file a complaint with the Internal Revenue Services.