What did you sign that states this? Most states are employee at will, so I get they can fire anyone for anything. I'd see if they've made exceptions before and what the details were, cite that as a precedence and it wouldn't be very painful l, as HR would not want it to appear that their is inconsistencies within the organization.
A wage increase may be worth negotiating especially it being annual review time. 5% seems to be the number these days people are using.