However, at most companies, there's no formal requirement that you do so. Most employment in the United States is called "at will", which means that your current employer can fire you at any time and for any reason (except those that are prohibited under law).
Do You Really Need to Write a Resignation Letter? Why Write a Resignation Letter? Do you really need to write a formal resignation letter? The short answer is that most of the time, no letter of resignation is necessary. Many people do believe that as an employee you need to formally resign from a job by writing a formal resignation letter to your current employer.