My question involves employment and labor law for the state of: Maryland

Today my boss told me that she wants me to complete a 16 hour training over the course of one weekend. She told me that she will pay for the class, but that I will not be compensated for my time in the class. I work in a daycare and I have already completed the required training. This is just something extra that my boss wants me to do. I was under the impression that all training has to paid for. Can anyone help me?