>If labor is cheaper elsewhere, can they get them to strike together? Are they trying to connect with them?

The Taft-Hartley Act actually made that illegal. Strikes can only be engaged in between the shop being struck against, and it's respective Union. Network effects are apparently too destructive to be used by anyone except for the people raising money.

In short, no industry blacklisting of Union members/organizers by employers is allowed, and no secondary striking by other shops' laborers are allowed to be organized.

This legislation was enacted due to some rather poorly timed strikes during WWII if I recall correctly. Or at least that's what I've read.