Union or Non Union Help Please.

I’m in the Marine corps right now and i’m thinking about doing electrician when I get out in a few months. Why do people go Union or Non- Union, I will be located in New Jersey. Please give ur input on anything of why i should do either or. What are the benefits and pay and hours? Do I get laid off of work and have to collect unemployment? Will I have a stable job when I get out of the military?