Traditionally our store is closed on Christmas day - with pay. This year management has announced that we will also be closed on Christmas eve. This day is to be taken as a vacation day or if you don't have any PTO available, it will be taken without pay. There are no options. Is this legal?

Exempt Salaried employees only have legal restrictions on having their salaried docked, which would include holidays. There are no other such restrictions on other types of employees.

http://www.dol.gov/dol/allcfr/ESA/Title_29/Part_541/29CFR541.602.htm