A warning letter is an official document issued by an employer to an employee to address a specific performance issue or misconduct. It details the nature of the problem, expectations for improvement, and consequences if the behavior or performance does not change. The letter aims to formally notify the employee of the issue, provide clarity on expectations, and document the incident for future reference. It may include a timeline for improvement and is typically signed by a manager or HR representative. Warning letters are used to correct behavior or performance concerns while maintaining professionalism and clarity in communication.