It needn't be a union.
The higher gun control areas seem to also have higher levels of corruption, in general. And, cities owned by unions, like Philly and Detroit, seem to have common threads so I do believe that there is a connection. I strongly feel that the RKBA does not stand alone and it's barely scratching the surface (and is a sympton of) larger/deeper issues.
In politically entrenched cities, like Chicago, the power base is different but the intentions are the same. Unions rank up there with bankers and insurance companies but the top of the socialist heap is the Daley family/machine which has it's tentacles in Cook county, Springfield and if Obama wins, Washington. Don't ever forget that Hillary is a native of Cook County and is supported by the Daley machine. Brother Daley was p/o the Clinton Admin. Now they sit waiting to see which of their puppets gets the nod. Unions probably aren't second tier players here, imo. Guess why the two largest insurers in the U.S. are headquartered here. Pliable government. Pay attention to the Rezko case and see a small, nay tiny, slice of the corruption that exists. Obama suggests "Change", how about change in local government? This is the Mayors ..nth term.
Oh and for the edification of those paying attention...
"Stephen Halbrook, one of our leading contemporary Second Ammendment scholars, express it this way: "The two categorical imperatives of the Second Ammendment - that a militia of the body of the people is necessary to guarantee a free state and that all of the people all of the time (not just when called for organized militia duty) have a right to keep arms - derived from the classical philosophical texts concerning the experiences of ancient Greece and Rome and seventeenth-century England. Aristotle, Cicero, Machiavelli, and the English Whigs provided an armed populace with the philosophical vindication to counter oppression, which found expression in the Declaration of Independence and the Bill of Rights. In this sense, the people's right to have their own arms was based on the philosophical and political writings of the greatest intellectuals of the past two thousand years."2
Although it is correctly understood that the cradle of philosophical thought regarding the right of a free people to bear arms was the classical Mediteranean civilizations of Greece and Rome, a very early and rare expression was unearthed in ancient China:
{Your subject has heard that when the ancients made the five kinds of weapons, it was not for the purpose of killing each other, but to prevent tyranny and to punish evil. When people lived in peace, these weapons were to be prepared against emergencies and to kill fierce animals. If there were military affairs, then the weapons were used to set up defenses and form battle arrays.}3
2.Stephen P. Halbrook, That Every Man Be Armed: The Evolution of a Constitutional Right 8 (1984)
3.Emperor Han responding to a petition from the Imperial Chancellor Kung-Sun Hung to take arms from the people.124 BC from American Rifleman 14 January 1959)
Excerpt from "The Second Ammendment Primer" Les Adams 1996