Most of us are at-will employees, non-union employees and those without employment contracts. In general, at-will employees may be terminated, suspended, demoted, or disciplined at any time for any reason. There are a number of important exceptions to this rule. It is unlawful, for example, to terminate an employee because of their age, gender, race, sexual orientation, etc., or for reporting employment discrimination or harassment. It is unlawful to terminate an employee for reporting what they reasonably believe to be illegal conduct or safety violations by an employer. It is unlawful to terminate an employee in order to deprive them of sales commissions or other earned income or bonuses. It is unlawful to terminate an employee for doing what the law requires (for example participating in jury service), or requiring them to do what the law forbids (for example, provide false information to a safety inspector). There are many more exceptions to this rule, so it is important to contact an attorney to determine your rights.
Statutes of limitation are short, often less than a year (even shorter for federal employees), so it is very important to contact an attorney as soon as possible.