I spoke with my brother about hearing that non-union utility folks from AL had been turned away from NY/NJ. I figured him working 30 yrs at a utility company (gas side, but also up to his eyeballs in safety committee for years so knows lots about the electrical side as well. This utility was non-union for years and years, and has now been union for almost 10 yrs. He has not heard the story, but would believe it about NY but more doubtful about NJ. But he did provide insight....
Apparently there is a reason why crews from other states (union or non-union) don't like to work together -- safety.
At first blush it might seem like it would be easy enough to incorporate other line people in with the regular crews, but when you factor in that these folks are working with high voltage and could potentially kill people 5 miles away by not following safety protocols should give you pause.
While union employees all have to go through the same education and training standards, the non-union linepeople may/may not have had the same level of training. Doesn't mean "go away", but may make a difference in what they are permitted to work on.
Bigger reason has to do with each company's SOPs being slightly different. While the outcome would be the same in 6 different companies, they may all have totally different means to get the job done, including when/how they deenergize the system or bring it back on line.
Most of the electrical companies have rules against working in a "blended" (read multiple companies) crews and that jobs/sections of the grid need to be designated and assigned to one company (home or visitor).
So, while I cannot confirm nor deny if the story is true or not, this is at least new information for me in terms of "why"