http://www.irs.gov/individuals/article/0,,id=106778,00.htmlIf you suspect or know of an individual or company that is not complying with the tax laws, you may report this activity by completing Form 3949-A. You may fill out Form 3949-A online, print it and mail it to:
Internal Revenue Service
Fresno, CA 93888
If you do not wish to use Form 3949-A, you may send a letter to the address above. Please include the following information, if available:
Name and address of the person you are reporting
The taxpayer identification number (social security number for an individual or employer identification number for a business)
A brief description of the alleged violation, including how you became aware of or obtained the information
The years involved
The estimated dollar amount of any unreported income
Your name, address and daytime telephone number
Although you are not required to identify yourself, it is helpful to do so. Your identity can be kept confidential.
Frequently Asked Questions - 1.13 IRS Procedures: Reporting Fraud
How to Report Abusive Tax Promotions and/or Promoters:
Complete the referral form which documents the information necessary to report an abusive tax avoidance scheme. The form can be mailed or faxed to the IRS address and fax number on the form.
How to Report Abusive CPAs, Attorneys or Enrolled Agents:
Report suspicious actions by tax professionals to the email address of the IRS Office of Professional Responsibility.