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).
What Should My Letter of Resignation Say?. If you're not sure of how to write a resignation letter, that's normal __ it's certainly not an everyday task. Take a look at a sample resignation letter, or a few if you want to explore different options. In our view, the shorter the resignation letter, the better.