Properly filling out Form 3949-A, Information Referral, requires identifying the person or business being reported, including the tax ID number if known, a description of the offense and the year(s) the fraud was committed. The person filing the form does not have to identify himself, explains Gelman, Rosenberg and Freedman.
The Internal Revenue Service, or IRS, makes Form 3949-A available on its website or by mail. It is used to report suspected false exemptions or deductions, kickbacks, altered tax documents, unreported income and organized crime. For unreported income fraud, the IRS requests an estimate of the money involved. Reports of tax fraud cannot be accepted by phone, but a letter that provides the same information as Form 3949-A is acceptable, according to the IRS.