well i can't speak for Local 48 in Portland, but i would say Being Union is less demanding than working non-union. I'm assuming you mean construction work. My past experiances with Union contractors is there not much different than non-union in they want to install the job as fast as they can and get as much done as possible. On big jobs you will have Formen that are Union guys such as yourself stepped up from the work crew. in my past experiance they look out for the crew as much as possible but they still have a job to do for the contractor. On small jobs such as working for local shops it's more demanding in that some guys try to impress the local contractor more so they won't get laid off. On big jobs everyone knows they will eventually get laid off so it's not that big of a deal.
But from past experiance on Union Jobs you still have to work hard but i'd say it's not as demanding as non-union. Plus you'll get better benifits than most all non-union jobs pay. Being Union pays better wages,insurance,retirement,and some locals pay vacations and annuities as well. When i worked Union Construction i never punched a time clock. Once i got on a local plant the is Union ,I am not punching that time clock.
Call up the local Business Agent in Portland they can fill you in on wages,benifits, and any questions you may have.