Does the Library have the right to fine me?

Obviously businesses can fine borrowers for late returns, but I went to the library several times to return the borrowed books, and there was no night return box or anything... As such I built up some fines, do they have the right to issue fines even when I tried to return the books, (when I went there after hours even the librarians were at the library watching me and wouldnt take the books back :(