I am a part-time local sorter/cover driver. Some Friday nights I am pulled off the sort and forced to run the PM air shuttle when all full-time drivers refuse to run it. The union book says that no part-timer shall work if there is a full-timer on the premises. I have always been under the impression that the work was forced on the lowest seniority employee that was already on the clock as a driver. Am I correct, or do they have the right to force me to run the shuttle? Any information will be helpful.