I wrote an essay on this. I said that the human rights issues in this book was lack of education and health care, and unfair pay. Lennie seemed to be lacking academically and there were cases where Lennie was hurt but was not taken care of while Curly was hurt but did get medical help. Also the pay is unfair because there is a very clear difference between the well-being of the workers vs the owners of the ranch.
Hope this helped, good luck! :D