Your employer can lower your pay as long as in doing so
1. You are still paid at least the federal or your state's minimum wage (which ever is higher is the one they have to go by),
2. They don't violate a union contract you are covered by,
3. They don't violate an employee contract you are covered by (usually only senior managers or officers of companies have these),
4. They don't lower your pay due to discriminatory reasons (i.e. due to your race, religion, sex, etc),
5. They don't violate the Fair Labor Standards Act, which has some wage requirements for certain employees that are considered exempt from this particular law.