The fact is that, yes your employer can schedule you to work overnight. While an employer will try to schedule an employee according to the employee's availability, it can and will always schedule employees has to its needs. In most instances, an employer has a great deal of discretion in setting the terms and conditions of the workplace. This includes who and when to schedule for hours of operation. For their part, an employee can choose to work for an employer or not. This is known as "at will' employment.  Exceptions to the above would be if scheduling you overnight violates existing company policy, the terms of an employment contract/union agreement, or constitutes some form of actionable discrimination.Bottom line, an employer can discharge an employee as it sees fit - this means for any reason or no reason at all. Hopefully, you can resolve this matter or else you risk losing your job.