Gather details on the fraud you are reporting. Try to get the taxpayer ID number, the dollar amount involved, the length of time it has been going on, what is going on and how you found out about it.
Get Form 3949-A, which is optional. This is an information referral form where you can detail the suspected fraud. Directions come with the form, which you can get from the IRS website. Once you fill out the form, print it and mail it to the IRS at: Internal Revenue Service, Fresno, California 93888.
Mail a letter to the IRS if you do not want to use Form 3949-A. Include all of the details that you have gathered in relation to the suspected fraud. Also include your name, address and telephone number if you wish to be contacted. Send the letter to the IRS at: Internal Revenue Service, Fresno, California 93888.
Alert the IRS to abusive tax promotions, which the IRS also considers fraud. You can accomplish this with a referral form. Fill out the form with the fraud details and either fax or mail it. You can mail it to: Internal Revenue Service Lead Development Center, Stop MS5040 24000, Avila Road, Laguna Niguel, California 92677. Or you can fax it to: 949-389-5083.
Report abusive tax professionals via email. Email the IRS Office of Professional Responsibility at firstname.lastname@example.org.