Can an employer force his employee to relocate?

I signed my employment contract in Georgia with a staffing company. I am a full time employee. my contract stipulates that I need to relocate whenever the company requires me to. Now I was assigned by the company to one of their client here in Seattle, and settled down here for 9 months, my wife enrolled into university classes....but then my company wants to re-assign me to a different location (Texas) now...I am refusing to relocate, and the company said I am breaching the agreement contract! can a company force an employee to relocate? if the employee refuse to relocate, would be this a good reason to fire?