Pros
After working for a year, you do get benefits. The union is meant to watch your back and they do intend to do it, but it will be on you to learn everything you can about how and when to get in contact with them. If they're looking for drivers, you can actually move up into a really decent paying position quickly.
Cons
Zero training in my group (They legitimately explained to us that we weren't going to finish the mandatory training process and asked us to sign documentation saying otherwise.) Management will do everything they can to keep you separate from union officials, and go out of their way to keep you in the dark about your rights as an employee. They will then make every attempt to violate them. Safety is an afterthought. I legitimately had a coworker lose a thumb. These cons had more to do with my immediate supervisor and his direct superiors than the company itself though, so keep that in mind.