for myself, the line is usually drawn right around how a boss would respond to you stepping out for an hour to deal with something at a normal non-critical time

for myself, the line is usually drawn right around how a boss would respond to you stepping out for an hour to deal with something at a normal non-critical time (or leaving early, or arriving late). If they're prying trying to figure out what could possibly be so important that I dare disrespect them like that, its usually indicative of a severe culture problem between management and workers. If they trust me as a professional to meet my deadlines, then it's probably not much use to unionise.