Tough thing to do given the nature of the business. As a union "organizes" the workers, the transient nature of the business would make this difficult. The "one week we're here, the next week we're there and the following week we're somewhere else" type of workplace makes it difficult to make the resources available, and almost impossible for the people to go to bat for the members to be able to effectively do anything.
Think about some of the bigger, multi-unit shows. One week a ride might be on Unit A, next week it might be on Unit B. The larger of an area the route covers, means that every time they cross a state line, the laws and rules change. Makes it rather difficult to help, even if the communication and resources are there.
Another point that no one has mentioned, and would work against the shows and the employees is the demands of a union local. As an example, one union local covers X County, and another union local covers Z County. A show based in X County with employees represented by the X county local has a date in Z County. The union local for Z County says, "You can come in and set up, but each ride has to have a member of our local on it". Now the carnival operator already has a full crew for each ride, that work well together -- everyone knows what they have to do. He's got a couple choices - 1) he can hire someone to work each ride from the local (and now has too much extra help on the payroll), 2) he can hire someone to work each ride from the local AND lay off one of his own guys on each ride, or 3) he can tell the local where to shove it, and face a picket line, which his own unionized employees might (and probably will) refuse to cross. Each one of these scenarios are bad for the biz in general.
Don't laugh and say that this will never happen, as it happens every day with the construction trades in the NY City metro area. Sometimes scenario #1 happens, with the "extra help" doing nothing but just being on the job. More often, scenario #2 happens. Usually scenario #3 doesn't happen (nobody wins).
There may be an interest in unionization out there in the biz, but I would venture to say that given the way things work, a unionized carnival lot would not be any better in the end than the same lot that is non-union.
That's just my two cents worth....
"A journey of a thousand miles must begin with a single step." - Lao-Tsu
"Faith is taking the first step, even when you don't see the whole staircase." - Martin Luther King Jr.
"Only those who dare to fail greatly can ever achieve greatly." - Robert F. Kennedy