The process for reporting a tax exempt organization for review to the IRS is fairly straightforward. It requires Form 13909 (available here) to be completed, then submitted, either through:
TEGE Referrals Group
1100 Commerce Street
MC 4910 DAL
Dallas, TX 75242
California requires the form CT-9 (available here) to be mailed to Sacramento. Please mail to:
1300 I Street
P.O. Box 903447
Sacramento, CA 94203-4470
California also recommends contacting some, if not all of the following entities.