The article also shows that Trump is still using illegal immigrant labor in his current jobs. If you had actually read the excerpt you would see that it talked about the fact that illegals are currently working on his DC project.
Is DC a union only area? Hell, most contractors in Nashville use illegal Mexicans and have since 2000 because Americans rarely work. Try to hire American roofers? Try to hire American drywall types. I cannot find them as the owner might be American, but; his labor is illegal Mex.