According to the IRS, its toll-free fraud hotline is 1-800-829-0433.Anybody who suspects or knows that a business or individual is in violation of the tax law can order a form #3949-A, called a referral form, at the aforementioned number.
Form 3949-A from the IRS is used for reporting a person or commercial establishment that is suspected of claiming false deductions, is receiving kickbacks or is failing to report income or pay their tax, according to the IRS. A failure to withhold tax can also be reported on the document.
The form can be printed and mailed to the IRS at its Fresno, Calif. address. In lieu of filing the form, a letter can be sent to the same address that gives the name and address of the tax violator, his employer identification number or Social Security number and a brief overview of the alleged violations.
Include how the information was obtained and how long it has been going on. The estimated amount of unreported tax income should be included in the correspondence as well as the sender's address and telephone number.