Can my employer move me to lesser paying job within the company without my agreement?

Having worked shifts for the last two years ( three shift system) with the added bonus of shift allowances in the same job for the last seven years quite happily, my supervisor has told me that he intends to move me to another department, permanent days , no shift allowance after replacing me with a new employee to fill the gap (Created by moving me) on my current job….. I stand to lose a significant amount of money from my weekly wage……. Can he do this without my agreement?? I think not… your thoughts please…..