Pros
The more seniority you get the more job options you have. Good health insurance. Job security in the welding department compared to other jobs. Able to move around if you want inside your district according to seniority. Railroads transport everything so it's a line of work thats steady even during an economic down turn. If your in a craft; you belong to a union and you do have some protection and help if you get into trouble or get hurt. How much help is debatable.
Cons
The rate of pay is not equal to the amount of responsibility you will have in certain positions. There's no reward system for the amount of work you accomplish other than the buddy system. It takes a alot of union force and alot of time to get any kind of raises and meaningful compensation out of the company usually several years. They demoralize their own work force by saying one thing and doing another with the actions they take without realizing it alot of times.