That is a broad generalization. I know lots of trades people that saw their disposable income decreased after becoming unionized. Additional deductions on pay cheques to pay for union reps, and business administrators, & bureaucrats, and time off (not working) between large union projects and while on strike. I was in IBEW Local 105 for 12 years and at best they acted like clowns. Union meetings were piss ups and the old boys (stuck in the good old days) would rather work 6 months a year and sit on their the rest of the year. I was in a small company that used all IBEW propaganda for fire starter. I never spent a day on the picket line and we went through 2 strikes - I left the tools and got into electrical sales shortly afterwards.
I do not think there is any real reason to have a union if you work in an office or a public servant - there are checks and balances in place for that. Listen to the teachers union moan and whine.......have they ever had a provincial government that they got along with? NO