Unfair does not mean unlawful. The management (or their designee) can assign shifts pretty much as they see fit. I recall working in restaurants and having the same problem. It sucked, but, unless I wanted to work elsewhere I sucked it up. At one restaurant they required that if we worked a Friday and/or Saturday night shift (the big money-makers for tips) we also had to work Sunday brunch (which pretty much guaranteed nothing). So, in exchange for the good nights we had to work a 4 hour nothing shift.

Bottom line is that about all you can do is talk to the person doing the scheduling or to their boss and ask that the good shifts be parceled out better. But, beware, that can always backfire and you may find yourself on fewer shifts as someone might decide you are a rabble rouser.