Based on my understanding, you really have no legal standing. As with every contract, you are required to perform duties as assigned. This especially is the case when you are paid additional money to fulfill the extracurricular aspect of your job. As a principal, I can have someone work a gate at a football game for "free" if I so choose (this has been litigated). Basically, you have two choices: 1) Do the job as assigned, or 2) don't do it and face whatever consequences are within your district's policy. One other item to consider is what type of contract you are on. If you are probationary, I would be very cautious. You can be let go at the end of your contract with no explanation except: "It's in the best interests of the district."

By no means am a lawyer and you should take that into consideration. If you are asking "should I consider legal action?," then you should absolutely contact your ATPE lawyer. I'm curious what they will say. (Please share for our benefit.)