SIU Benefits? Part time employee

I MAY be taking a job that would be part time, 4 shifts a week, adding up to 20 hours. It works out perfectly with my current full time job so gets me some experience and something for a resume while letting me keep my current salary level. It is a union job, I am wondering what benefits, if any I would get from SIU?

Also in general, how does SIU work about healthcare etc, vacation, etc?