1) You have no right to be paid for your unused vacation hours if you leave your job unless you have an employment contract which you do not breach or violate which states you get them under these circumstances; ergo, if you leave work voluntarily, they don't have to pay out your vacation anyway.2) They can't legally withhold your last paycheck unless you agreed (e.g. in a contract) to let them do this; employers may only withhold employee pay with employee consent or as required by law (e.g. court-ordered wage garnishment, in states allowing garnishment).3) They can, of course, sue you to recover the relocation bonus if you violate the contract.