My employer requires hourly workers to attend industry-relevant events outside of normal work hours and without pay. Is this legal?

Hello, I''m in Illinois and have been an hourly employee at my current position for about three months. When I began, I signed a contract stating I''d attend two industry-related networking events per month - outside of normal work hours - and, when I inquired, learned I and my co-workers would not be compensated for the required hours spent at these events. With hesitation, I signed the contract. Later, I discovered the expectation of uncompensated work by management ongoing. For example, hourly employees have been required to do everything from read self-help books to drop off pamphlets on personal time. I''m wondering of the legality of this form of unpaid overtime - particularly as it related to being bound by agreed upon contract. Thank you for your help!