Not much, most companies have a 90 day probationary period in which they judge your overall performance, attendance and abort to be trained to do the job. During this period, they have the freedom to let you go if they feel you do not measure up.
This all depends on the contract signed as different companies have different policies. However you can seek assistance from a person who knows or who is well acquainted with the law in the state you are in.
90 days is not promised. It is a time period to consider if you are worthy to meet company standards. They are not liable in any legal way to you during this 90 days. After 90 days they generally need to give you reasons for dismissal. If you live in a right-to-work state, they may not need to give a reason. They may not dismiss you for any discriminatory reason after the 90 days. Don't expect any rights in the first 90 days.