As a general rule, IF the contract to which you refer is a contract for a definite term (e.g. a one-year contract) and specifies your position and/or pay, they cannot change your position or pay unless the terms of the contract itself permit them to do so--that is, they are bound to the contract for the duration of it, and can only do what the contract, by its plain terms, permits.But you write that you are on a reservation. Reservations are semi-sovereign governments with their own laws in relation to many things. If the law of this reservation would permit them to ignore the contract's terms, they may do so. You need to consult with an attorney familiar with this reservation's laws to confirm your rights. If you have the same rights under reservation law as you would have elsewhere in the U.S., then you are guaranteed whatever the contract gives you, and could sue for "breach of contract" to enforce those rights (though you'd have to sue in tribal court).If you are not protected by a contract, then they can change your pay and position at will. Pay, position, duties, title, benefits--even whether you are employed at all--is under employer control except to the extent the employee is protected by a contract.