What To Do When Your Job Ends "At the Will" of the Employer
The at-will arrangement for employment goes both ways. You can resign from a position if you don't feel it suits you. Your employer can also end your employment abruptly if you don't suit them. The only thing they can't do is fire you for a federally protected reason, such as your age, religious preference, nationality, gender, etc.
But they can terminate your employment for other reasons at any time after you sign up with them. In fact, they can pull the rug from under you before you even make it to the office if they so desire. What could you do in that situation? Not much.
Ask Them Why They Chose To Terminate You
It's natural to want to know why your employer cut you before giving you a chance. Thus, you can reach out to the hiring manager first and then go through the chain of command. Ask his or her manager if you can't get an answer, and then move to the next level. Be aware that they might not answer your question or explain anything to you. You might even get an unsatisfying response.
Speak To a Human Resources Representative
The human resources department sometimes plays a mediator between the employer and its employees. There's nothing wrong with contacting them to see if you can get some answers. Maybe you can apply for another job there, or they can fit you into another department. Alternatively, you might get a generic "we're sorry" response.
Speak To an Attorney or Organization That Can Help
You can contact a legal specialist or an organization that protects workers if you feel your termination involves discrimination. They can lend you an ear and collect your documentation to help you regain your position if the case is strong enough.
Think about whether that particular job is essential to you and handle it accordingly. There's usually nothing wrong with an employer saying "no thanks," but you might have a cause to pursue a case if it pertains to your protected class.