Is this illegal ?

My job won’t let me go light duty (I’m a nurse assistant I lift and roll really heavy people even if they aren’t heavy lots of them are contracted) I work night shift so it’s a little easier. But I have a note from my dr saying I’m not supposed to lift more than 20 pounds. My job said “there’s no lifting on night shift so I don’t need to be light duty”. We are short staffed as it is but I physically can’t roll people anymore. Can my job really refuse me light duty???