I didnt get a chance to read all replies so I dont know if its been
mentioned.

Working for free... illegal? Not quite, but it opens them up to a
whole world of trouble. If you are an hourly employee, you should be
paid for your hours. Ive been involved in college internships, and the
companies who take on college students in an un-paid arrangement are
hypersensitive about verifing that the students are actually recieving
credit, otherwise they are getting nothing for their time, and can
sue. There is a solid legal argument for you to demand payment for the
hours you have worked.

The fact that management would put themselves in a position where they
would have to convince a judge or mediator why they werent paying you
is risky and down right stupid.

My advice is this (if you dont want to do it)... refuse to do it, and
if they fire you for it, that would be solid grounds for a wrongful
termination lawsuit.