My Rights!!!

So I am a little mad at the moment. Yesterday I came into work and notice a hand written letter to me from the supervisors. It proceeds to say that my hours are going to be cut do to another worker coming back from medical leave. First I was mad because they tell me in a letter and it wasn't even typed, it was hand written at the bottom of the schedule log. Secondly I have been a full-time employee for over two years and to only cut my hours no one else, that is not right. Now I left a letter with our HR lady and she did leave a message (I was sleeping when she called) apologizing for the rudeness of the staff. She said she would work with me in making sure that I have shifts to work. I just feel so blind sided with this and Jeff has been looking into employee rights. We are keeping all our documents that I have received and hopefully everything will work out in the end. Any advice would be good right about now, so please let me know if I should do anything different or make sure I am covering all my bases.