Raise

The company I work for decided to give us employees an upgrade in our rate of pay. My boss pulled me into his office and confirmed that I was getting the raise and told me what my new rate of pay would be. This pay period I was not paid my new rate, however other peoples new rates were calculated in. Is it against the law to promise a raise and then take it back?.. I don't know If this is the case, but I'm talking to him about it the next time we work together which is Tuesday and I want to know if I have some legal backup to throw at him if he tries to take it back.