Below is a sample union resignation letter. You should check your union's constitution and bylaws to see if it is specific to whom a resignation must be sent.How to Use a Police Officer Resignation Letter (5 steps). Notify the Chief of Police; Give Reasons; Date of Resignation; Submit Letter; Return Items. 1. This letter of intent must reach NAVPERSCOM no less than 6 months prior to the first day of the month of an officer's PRD. Learn how to write a professional resignation letter with our step-by-step guide, easy to use templates and helpful tips.