Is the supervisor liable for researching workmans comp health restrictions prior to assigning a person to a position??

I had a back surgery in 08 and have been assigned to a position that has required me to climb steps which climbing is a violation of my work restrictions....Due to feeling that the supervisor knew of my injury, due to me making previous managers aware, and that if I failed to comply, that I would be written up for insubordination, since I have seen retaliation from the new supervisor, I did what was expected of me, and suffered in silence for 1-1/2 yrs....I am now being threatened by my supervisor with a union defense, as I have been threatened in other ways, in the past by her, and do not know if I am liable in the eyes of the gov't agency and law, or if the supervisor is liable for ensuring that the employee she assigns to a position is capable of safely doing so, by researching her employee's medical histories from the employer's medical records facility? How does the law look at this, and is the supervisor in the wrong for not checking medical records prior to assigning me or am I?