Who should I call to report someone who is not filing tax returns?
If you believe someone is violating federal tax laws, you should contact the IRS at 1-800-829-1040 for the Criminal Investigation Hotline in your area. If you prefer, you may provide your information in writing to your local IRS office, or the Criminal Investigation Branch at the service center where you file your return. Refer to your tax package for the address of your service center.