You can find the CP or LTR number on the right corner of the letter. The primary letter we use to request information about a return is Form DTF948 or DTF948O, Request for Information (RFI).If you did not earn income from work you are not required to submit an IRS Verification of Nonfiling letter. The letter applies to identity and tax return verification ONLY. Prospective Electronic Participants must complete a LOA for electronic filing of Forms 720TO and 720CS. Two types of sample letters are provided below. This letter is a self-correcting letter. The goal is to have you, as the taxpayer, self-correct. If you received a letter from the IRS, don't ignore it. Follow the directions on your letter, it includes all the information you need to respond.