What this notice is about Important Information about your child's Adoption Taxpayer Identification Number (ATIN) - Your child's ATIN expires in 3 months. What you need to do Complete Form 15100, Adoption Taxpayer Identification Number (ATIN) PDF Extension Request, included with your notice if you received a Social Security number (SSN) for your child, or; Apply for a one-year extension of this ATIN by completing Form 15100, if you don't have an SSN. Detach notice stub, mail it with Form 15100 in the envelope provided. If you prefer, you can fax it using the information provided on the form. You may want to Call us at the number listed in your notice. See additional information on Adoption Taxpayer Identification Number. Frequently asked questions What can I do if I don't have a Social Security number (SSN) for my adoptive child? You can request an extension before your assigned ATIN expires by completing Form 15100 included with your notice. The extension is only valid for 1 additional year. Reference Tools Publication 1, Your Rights as a Taxpayer Full list of tax forms and instructions Need Help? You can authorize someone to contact the IRS on your behalf. See if you qualify for help from a Low Income Taxpayer Clinic. If you can’t find what you need online, call the IRS number at the top of your notice or letter.