Just out of curiosity, or maybe I'm not understanding, isn't that against several federal laws?
Yes and no, most business based unions can easily violate anti-trust laws by squashing competition.
The most common form of business based union would be a corperate banking union composed of multiple entities (individuals and companies) to form a cohesive company, or labor unions that act as companies globally. iatse, for example is rather well known for acting as a hiring company for the entertainment industry where none of the iatse members are really hired by the production company but hired by iatse and iatse negotiates rates and business details "on behalf" of the members ... theatres, films and the other entertainment venues and productions don't have to be an iatse "house" or production ... but they generally all are even in non union states due to the fact that they really don't have any actual employees. (in theatres, concerts, etc ... the production company rents the facilities, hires iatse to run the show in the venue, etc ... leaving every bit really seperated from every other part of the end result)
Pretty much when it comes to business unions it really is ok as long as the end result doesn't cause dominance in a market ... most trusts and unions that are formed on the business end are almost always in the end result to cause legislation changes and reforms, now I think they range anywhere from "Super PACs" to Lobbyists to even industry "councils" ... pretty sneaky if you ask me.
Sadly, there are a few ways that companies enter a sort of business union/trust without violating anti-trust laws and can still operate outside those laws ... basically they buy stock in the other company ... enough to get on the board of directors for each others company and can thus do some really nasty things. Most anti-trust laws were formed because companies would almost force out competition by doing things such as buying out resources of competing companies to create a vacuum on commodities, collectively drop prices to below what the competition could support, buy multiple other companies (including dealers, suppliers and production companies) in the attempt to cancel standing contracts and raise rates on competition and other nasty things to basically become a monopoly on an industry. Anti-trust laws were established to be able to legally break a company into individual pieces to create competition in the marketplace ... happened to bellsouth .. almost happened to microsoft (microsoft just had to pay out to anyone who used their software during certain time periods ... i enjoyed getting my check for windows 3.1, four copies of 95, all the copies of 98 and all my NT OS's ...)