Is it illegal for a bank to cash a check before the date marked on the check?

I wrote a check to my brother dated for the 28th and his bank cashed it on the 27th. I have the cancelled check and a copy of my statement showing an overdraft fee due to this mishap and am planning on taking it all to his bank to get reimbersed. I'd just like to know if what they did was illegal, unethical, or possibly just their policy. His bank is TCF.