Labor unions don't outsource work to China, they are just one of the main reasons the work is outsourced to China...
I'm not sure how you outsource construction.
How so?
Because unions are a royal PITA for supervisors and management. They make doing business more tedious and difficult. They are just a legal "protection" scam that was invented by organized crime.
The same unions that run actual aporenticeships, pay a living wage, sued for a 40 hour workweek, and a retirement that offers a meaningful quality of life after your working career? Note! Not saying labor unions are perfect, but imagine only scab labor.