Is there any recourse for experiencing a huge pay cut from changing job description?

I am an hourly Assistant Manager of a retail establishment. I have worked for this company for over 6 years. In duties section of the ASM job description it states that I am required to work a minimum of 48 hours per week. 8 hours of that is overtime. The company is about to change the job description to eliminate the minimum 48 hours. I will end up losing over $10,000 per year. I spoke to my district manager and was told the decision was because other ASMs were not working those hours anyway. I audited my hours for the last two years, and even after subtracting all holiday, vacation, and sick hours, I worked well over an average of 48 hours per week. Is there nothing I can do about this huge pay loss?