An FDA Warning Letter is a formal notification from the U.S. Food and Drug Administration (FDA) sent to companies that have violated legal or regulatory requirements. The letter highlights specific violations identified during an inspection or review and demands that the company address the issues promptly. Receiving such a letter is serious, as failure to comply with the stipulated timeframe for correcting the deficiencies could lead to the denial of an approval or a complete import halt. Warning Letters are publicly accessible on the FDA's website.
https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/compliance-actions-and-activities/warning-letters