When you say "contact the labor board," what do you mean? The PA Labor Relations Board only deals with disputes related to management and unions not covered by the NLRB, and if OP has a union, they shouldn't be coming here with questions they should be taking to their union instead. This advice is not helpful because the PLRB probably cannot help OP.

Legally, without a contract stating otherwise, your employer can absolutely fire you for refusing to work 12 if you're scheduled for 8. You'll get unemployment, sure, but they can fire you. The answer to this is right on theFAQ at the Department of Labor and Industry (question 5).

I agree that the mandate to work overtime is bullshit and hate that employers are allowed to get away with it, but that's labor law in just about every state in this country, PA included.