"Unpaid" and "voluntary" can run into some gray areas of the law. Where it becomes a problem is if an employment decision is based on attendance at those "voluntary" meetings. Six months from now business slows down and the company needs to lay someone off. "You know Joe Smith? That guy never comes to training meetings. I'm not sure he's serious about learning his trade. Maybe we ought to let him go." Or Joe, Bill, and Steve are let go (just because their mediocre electricians). They get to talking and they realize that none of them attended those "voluntary" training classes (which is rather likely). Then Bill remembers an ad he saw on late night TV about lawyers who help people. All of a sudden the company is spending ten grand trying to prove that Joe, Bill, and Steve were just lousy electricians.
My gut reaction is that any time you have hourly employees you need to pay them for every hour worked, even if it's just a meeting. It is a two way street and "good" employees will want to learn more about their craft even if their not getting paid. But it does show that the employer is serious about training.
