49 CFR 107.309 - Warning letters.
(a) The Associate Administrator may issue a warning letter to any person whom the Associate Administrator believes to have committed a probable violation of the Federal hazardous material transportation law or any provision of this subchapter, subchapter C of this chapter, or any special permit issued thereunder.
(b) A warning letter issued under this section includes:
(2) A statement that the recurrence of the probable violations cited may subject the person to enforcement action; and
(3) An opportunity to respond to the warning letter by submitting pertinent information or explanations concerning the probable violations cited therein.