The Nuts and Bolts of Dues
There is tremendous variation from one union to another as to how dues amounts are set. And it is quite possible that the different components of your union dues (local, district or other intermediate body, and national/international) are calculated using different formulas and changed in different ways. The formula used for determining what your union dues are, and the mechanisms that are in place for making any changes, usually are found in the constitution and bylaws of the union at the various levels.
—Adapted from The Union Member's Complete Guide, by Michael Mauer