Employment at will is a very common practice. In fact, if potential employees read applications very carefully, it is typically stated on the application. It is probably one of the least understood practices of the mechanics of employment.
The basic premise when you are employed at will, is that the employer does not need a good cause to fire you. It is the norm, not the exception. It should be noted that Montana is the only state that opts out of the at will practice. In Montana, after a probationary period the at will clause no longer applies.
Just because you are an at will employee does not mean that you have been stripped of all your rights. If you are an at will employee you have no binding contract about length of employment and you can leave at will. An at will employer cannot fire an employee for reasons that are illegal under state or federal law. For example, firing someone for race, religion or gender would be considered discrimination and that is not legal. You cannot be fired for reporting illegal activity that the employer has committed. You can not be fired for exercising a variety of legal rights. These rights might include the right to take medical family leave, to take leave in the military or to take time off work to vote or to serve on a jury.
With this being said, once an at will agreement has been signed it is hard to prove that your employment was terminated for an illegal reason. Many companies bundle the information in the general handbook. They may list a general list of guidelines and things that you will fired for. It is important not to just assume these are the only things that can leave you without a job. If you are unsure of your company, simply ask. If you don’t understand what you are reading, ask. If what the employer is saying is different than what the documentation states, ask questions. It better to know than to be blindsided.
Most people assume that if they do a good job and work hard they will not be fired. In general, that is normally the case. However, when times get tough at an at will company, all they are required to do is to tell you that they are letting you “at will”. Read all the company information. Just skimming through is not enough to tell what rights you have.
Again, since this is the norm, it is not something worth fighting. It is essential that you understand it to be prepared for the things that can happen and do your best to keep a job you love.