Federal and state laws protect employees from being fired for a variety of reasons. Taken collectively, they form the many possible grounds for a "wrongful termination" or "wrongful discharge" lawsuit.
Discriminatory firing based upon the "protected characteristic" of an employee is prohibited. Some examples of protected characteristics are: race, national origin, age, gender, sexual orientation and disability. It is important to note that different states recognize different sets of protected characteristics.
Firing an employee in retaliation for filing a complaint of discrimination or supporting another employee's complaint of discrimination is prohibited. Likewise, firing an employee in retaliation for refusing to participate in or exposing wrongful conduct of her employer is prohibited. In these situations, a victim of retaliation may be able to sue for damages, including lost wages, emotional distress damages and punitive damages.
Other illegal reasons for firing an employee include the employee's exercise of his medical leave rights (FMLA or NJFLA) and his absence from the job for a period of active military service.
While it is often said that New Jersey and New York employees are "at will" and can be dismissed for any reason or no reason at all, there are many "exceptions" to the at will doctrine. To discuss whether the exceptions may apply to your particular case, you should consult with an attorney who concentrates in employment law.