Can my employer changed my schedule after I fill out an availability form?

Actually, yes it can. While it will try to schedule you according to the form, in most instances such a form not a binding document. So while an employer will try to schedule an employee according to the employee's availability, it will always schedule employees has to the company's needs. The fact is that 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 quit. This is known as "at will' employment.

Exceptions to the above would be if scheduling at times for which you are not available violates existing company policy, or the terms of an employment contract or union agreement. Also, no form of actionable discrimination can play a role in your scheduling conflict.

Bottom line, an employer can terminate an employee as it sees fit; this means for any reason or no reason at all. So perhaps, you need to resolve this matter as best you can or risk losing your job.