The first thing you need to do is be honest with yourself. Did you make a mistake? Did you do something that was against the rules? Has your performance slipped? Do you and your supervisor have a personality conflict? It is important that you honestly assess what your actions were that caused you to be disciplined or warned, because you cannot correct problems that you do not acknowledge.
If you really want to keep your job, and in this economy, keeping your job should be your top priority, you will need to take certain steps to get back in your employer’s good graces. Immediately stop fighting with your employer. Even if you believe you have been accused of something unfairly, remember that as an at will employee, you can be terminated for anything except discrimination. Not fighting with your employer does not mean that you agree with his or her version of the incident that brought on the discipline. It just means that you acknowledge that your employer has the legal power to discipline you for anything and that he or she is looking at this incident from a different point of view.
Next, find out how much time you have been given to correct your performance or behavior issue. If you have been given a Performance Improvement Plan (PIP), there should be a schedule of things that you need to do within a certain time frame. Make sure that you keep to this time frame, and perform all the tasks required.
For those discipline actions that mention an incident and tell you not to do it again or you will be immediately terminated, the time frame to improve is immediately. Legally, if you repeat this action, not only will your employer be able to terminate you, but it probably can prevent you from getting unemployment benefits, as well.
If your employer has given you specific tasks to do to improve your performance, make sure you do them. While the tasks might be difficult and may cause you to put in extra hours, that is the way your employer has chosen for you to show improvement. If you do not know what is expected of you, find out. Go to your manager, and tell him or her that you want to work to improve whatever he or she found wrong.
Finally, pay attention to your attitude. Right now the economy is poor and companies are closing. This is not the time to stand up to an unfair employer over a disciplinary incident. The employer holds the power. Of course, if you can prove discrimination, you can always file a discrimination complaint, but filing that complaint does not help you keep your job.