Can a store charge you an ATM fee without disclosing it?

Our local grocery store has a few self-checkout lanes that I use often. The store does not accept credit cards. They only accept debit cards. My last 2 debit charges have included a $1 fee tacked on. I didn't really look for any signs about a fee last time because they hadn't charged us in the past. However, I looked today and didn't see any notices of a fee. There was also no notice on the electronic pad of a fee when completing the transaction. The pad asked if I approved an amount of $26.17 (the correct amount) and I said yes. However, my account shows 2 debits, one for $26.17 and one for $1 (grocery store atm fee). So can they do this or are they violating some law? I don't mind paying the $1 but it seems wrong that they aren't telling me about it.