Hi, I have been an on LTD for 3 years and when I recently requested a copy of my policy the case manager replied he is unable to release my policy plan, that I can contact the union and ask them for it. Why would they be “unable” to send a copy? Do I need to contact the union? I am confused.

You do have a right to see your policy. What I would recommend is that you email a representative of your union, your HR, and your insurer all at the same time (in the same email), and (politely) say that you'd like to see your policy. Keeping them all in the same email chain should prevent you from being given the runaround.