Does everybody in a particular labor union have to strike when others do?

Like with the SAG-AFTRA and the UAW strikes going on right now. Why does it seem like individual union members get shunned or villified if they decide to keep working instead of striking? Shouldn't it still be up to individuals in the union to decide if they still continue to work or strike?

Does everybody in a particular labor union have to strike when others do?
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