Just don't use the word Union!
Really great idea
If you don't mind my asking, what makes you say this?
What is being described is exactly how a local union system works. The local guys all have first dibbs on any work done within their jurisdiction. When the demand for labor becomes greater than the supply of labor, the companies in need of help have the ability to draw upon a vetted labor pool, from a much larger area than their own local market. Each local union has a building space that guys can go to to take care of the referral process and paperwork. Each local negotiates its own contract with the group of businesses in that area that choose to become signatory contractors. In this way, locations with lower costs of living can negotiate a fair price for the local conditions. This becomes a minimum standard, but there is nothing stopping a company from paying more, in order to attract help from further afield.
They do this because they're aware that it's expensive for someone to go on the road to work. The person who works on the road is usually paying rent twice, if they have a permanent domicile in their own local.
This arrangement also opens up the door to establishing retirement funds for the personnel that are associated with the union and not any individual company. I personally favor the idea of IRA's, because that money belongs to the individual and not the organization, as opposed to a pension fund.
Running the organization is probably an expensive proposition, however. It is also subject to being corrupted, because the person in the position of running each local has a lot of power and flexibility in how things happen, so it's necessary to pick honest, ethical people to fill those positions.
That's all for now.
Tim