Pregnant and dismissed because of need for light duty work

I am 4 months pregnant and due to some pregnancy complications, my physician wrote a note to my employer requesting "light duty". I work as a nursing assistant in a children's hopital that has granted light duty work to other pregnant women or injured employees. I only verbally relayed the light duty request to my employer who assured me that she would comply to the request. After my first shift of light duty ended, I was contacted at home and informed that I was being "taken off the schedule" until the light duty order was lifted by my physician. I was told that I would not be "useful" as a light duty employee and secondly, they did not have light duty work available. I have the original doctor's note that substantiates my request and my employer has only recently asked for a copy which I have not yet provided because of their refusal to give me a written statement explaining my dismissal. Is it legal to "temporarily dismiss" me on the basis of my VERBAL request for light duty? Is this discrimination on the basis of pregnancy? Thank you for any and all information you can provide.
Alisha Collier