If you want more hours and he is refusing, but hiring additional people, I do think you have a right to know why he won't give you more hours. And if he is hiring more people while refusing to give you more hours, I think you could, in this instance, go to HR and ask for an explanation. I think you have to push for an explanation, and be a little pushy, because if he's trying to skirt the discrimination then he's going to continue to not give you an answer. If you are in the US, you could file a complaint with the EEOC about discrimination, especially since he cut your hours directly after you requested he fill out paperwork for social security disability reporting. If he won't give you a direct answer of why he won't give you more than 2 days of work, then you need to take it up the chain, politely and respectfully, to get an answer.