"Insubordination:  Refusal to Carry Out an Order

   In order to uphold the dismissal (or discipline) of an employee for insubordination,
 arbitrators usually look for two components, both of which must be present:

1. a refusal to follow a direct, valid work order -- The order must be clear, it must come from
    someone authorized to issue directives, and the employee must understand it as an order.
   
2. a clear prior warning of the consequences -- The supervisor must clearly state the penalty for
   continued refusal to carry out the order. An employees' failure (as opposed to refusal) to
    carry out an order, or protest while carrying out the order, may justify a lesser charge than
    insubordination and, consequently, a lesser form of discipline, but would not, by itself, 
   constitute insubordination.

    The general rule for employees who are confronted with a work order they believe is objectionable,
unfair, improper, illegal or a violation of the union contract is: "work now, grieve later." There are 
some exceptions to this rule, such as when an employee has a reasonable belief that carrying out the 
work order will endanger the health or safety of him/her self or others."

from  CUE UNION