Since your state does require notification before a reduction, they'd owe you the expected amount, at least as far as salary is concerned. In some states where that is not true, many employers have done this, legally, paid the person for the last pay period ONLY the minimum wage for the hours worked. You need to file that wage claim with the state's department of labor wage and hour division, and can probably get paid a few dollars more. There's no charge to work with them, there's no attorney required, so it'd certainly be worth the time to see if the can be made to pay you this additional money they're trying to cheat you out of for spite from them.