I don't think that too many places anymore give you an early warning or a probationary period for firing. I think that they generally do for laying you off. However I am used to working in the aerospace industry, and things might be a little different. There is also a big difference between a "Fired" and a "fired for just cause". Also, whether the state that you work in is a "At will" state makes a difference. Most states are "at will" states today. In other words, they can fire you "at will", without cause or reason. Companies generally fire at will only when there is no recourse, and they fire everybody in the company, otherwise they open themselves up for possible discrimination suits, and other things that they would rather not go to court for. Why do companies fire? Ever seen a good worker fired, even though they lacked a good reason?. People are generally fired because in most states, maybe all, when an employee is fired, the company can hire in a replacement immediately. When a person is laid off, and they hire in somebody a little too quick, they are open to going to court. People are generally fired when the company already has a replacement set up, good to go, so to speak, and generally less wages, benefits, and getting rid of any seniority
that they would like to are the reason mostly.