Can your boss give you a raise and then just take it away because a co worker find out and wants the same

There is probably little you can do about this.  Your employer can give a raise and take it back, just as it can reduce/increase your hours, change your schedule, increase/decrease your pay, require you to work overtime (as long as it pays you), prohibit you from working overtime, etc.  However, what the employer cannot do is rescind or take away a raise becuase of your race, religion, gender, national origin, disability, age, or sexual orientation (or becuase you complained of discrimination.)   It is probably best to contact a few attorneys directly and that should give you a better idea as to what you can or can't do about this.