The union position would be in support of local labor, who make and cost more as opposed to the outsourced labor. In practice, I've seen mixed sides to all of this. Boeing itself is a very large, very litigious organization, and there's a lot of issues at play. Boeing is also a major military supplier as well.

In the end, it's probably at least partially true and very biased at the same time. I think the biggest arguments about unions are if they provide value, and if you are required to be part of a union in order to work in a given position/company. There've also been weird reverse-unions where the union is actually on the employer network's side. I've seen this happen locally with regards to nursing workers, the collective is member operated under the various hospitals and providers for fixed, down-ward driven rates.