First, ask to see your personnel file. In many states, employers are required to make it available to you. Make a copy of all reports and reviews in it. Again, some states require the employer to allow you to make copies. Make a list of every single document the file contains. That way, if your employer adds anything later, you will have proof that it was created after the events in question.

There are a number of ways to document events that happened. The easiest is to keep a journal in which you record and date significant work-related events such as performance reviews, commendations or reprimands, salary increases or decreases, and even informal comments your supervisor makes to you about your work. Note the date, time, and location for each event; which members of management were involved; and any witnesses who were present. Keep your notes at home or in a secure place.

Whenever possible, back up the notes in your journal with materials issued by your employer -- such as copies of the employee handbook; memos; brochures; employee orientation videos; and any written evaluations, commendations, or criticisms of your work. However, don't take or copy any documents that your employer considers confidential -- this will come back to haunt you if you decide to file a lawsuit.