Pros
Only pro to working at Cat is that if you have enough seniority, you may keep your job while they cut the workforce. That is if you can make a living without raises or any chance of promotion.
Cons
Honestly, if I were to list all the cons to working as a union employee at Cat, people would not believe they were true. Cat enjoyed record profits quarter after quarter until 2013, and management treated themselves to pay increases and bonuses each year. The average working guy was given only one 3% pay increase in the last five years (due to a new contract being signed by the union), and nothing else. No bonuses, no cost of living increase, no pension. Things like tuition reimbursement has been revoked, so no chance to improve yourself. Many more things could be listed, but you get the idea.