Locate the closest Taxpayer Assistance Center to you. You can find the CP or LTR number on the right corner of the letter.You can deduct a part of your medical and dental expenses, and amounts you paid for certain taxes, interest, contributions, and other expenses. Does anyone have sample letters to the IRS for different situations? Maybe one with code numbers and explainations. A request for a letter ruling should be sent to: Internal Revenue Service, ATTN: CC: DOM: CORP: T, PO Box 7604,. Ben Franklin Station, Washington, DC 20044.