Disobedience to an illegal order is not contempt. How you disobey can be construed to be contemptuous. You can refuse to obey an illegal order, but it must still be done with respect to the Office of the person giving the order. There is a requirement of decorum amongst the commissioned Officers. The proper statement would be stated as thus, "All due respect sir, but I cannot obey that order as it is a direct violation of my Oath and the laws of this nation."