Definitions for "Warning Letter"
The most serious FDA postaudit (after inspection) letter notifying a manufacturer of adverse finding and giving it 15 days to reply.
an official notice to a regulated business establishment that objectionable conditions or practices have been identified in their operations, that corrections are expected, and that failure to correct the deficiencies may result in further FDA actions
a serious notice to an investigator and demands development of effective corrective actions, with the threat of legal penalties if the actions are not impending