Dear Peoria, Arizona:
Arizona is a "right to work" state, but that doesn't mean quite what it sounds like. It means that an employee cannot be forced to join or maintain membership in a union to have a job.
Other than that, an employee can be terminated at any time for any reason that is not against the law or discriminatory. A reason that is against the law would be, for example, terminating an employee because the employee refuses to illegally dispose of hazardous waste. A discriminatory reason would be based on race, religion, national origin, etc. The Equal Employment Opportunity Commission (EEOC) has more information if you are interested, at http://www.eeoc.gov/. A discriminatory reason would include terminating someone for taking FMLA leave.
Under the Family Medical Leave Act (FMLA), an employee who works for an employer with 50 or more people - and 20 or more people at the location the employee works at -- is entitled to take up to twelve weeks unpaid FMLA leave, as long at the employee worked for the employer more than a year and more than 1,250 hours in the year before the leave. The employer is required to restore the employee to the same or similar job when the employee returns. An employee may also take intermittent leave, if approved by a doctor.
The FMLA leave gives employees the same rights to employment as an employee who is not on leave -- but not greater rights. An employee who would have been laid off if they were not on leave or had not taken leave can still be laid off if they are on leave or took leave.
Without knowing what exactly the company you are working for is doing, it isn't possible to know whether you were terminated because you were on FMLA leave or not. Here is the information for filing a Complaint based on violation of the FMLA: http://www.dol.gov/elaws/esa/fmla/fc.asp; the Department of Labor can investigate your termination and see if it arose from your status of being on leave.