26 USC 7522 - Content of tax due, deficiency, and other notices

(a) General rule 
Any notice to which this section applies shall describe the basis for, and identify the amounts (if any) of, the tax due, interest, additional amounts, additions to the tax, and assessable penalties included in such notice. An inadequate description under the preceding sentence shall not invalidate such notice.
(b) Notices to which section applies 
This section shall apply to
(1) any tax due notice or deficiency notice described in section 6155, 6212, or 6303,
(2) any notice generated out of any information return matching program, and
(3) the 1st letter of proposed deficiency which allows the taxpayer an opportunity for administrative review in the Internal Revenue Service Office of Appeals.