The article mentions that the union president was one A. Pappas, which got me curious. It turns out that bootblacking was predominantly a Greek immigrant trade in the early 20th Century. A passage from "Greek Americans, Struggle and Success", by Charles C. Moskos (1989) explains this, and also gives some idea of why the union was necessary:
A uniquely Greek mainstay in the early immigrant economy was the shoeshine or bootblack business. Throughout the North there were literally scores or even hundreds of shoeshine parlors in each of the big cities. For the boy who had no better choices, there was always work to be found in a shoeshine parlor run by a fellow Greek. From our present perspective it is hard to realize how lucrative a shoeshine parlor could be in the early decades of this century. It was a time when walking was more common and shoes became dirtier than today; it was a time when the full high shoe was in fashion and standards of shoe presentation more particular than at present. With the cheap labor of young boys, the owners of bootblack establishments could do quite well indeed. Some of the more enterprising owners managed to set up chains of shoeshine parlors.A 1994 article in the Journal of the Hellenic Diaspora takes an in-depth look at the bootblack trade and early 20th century attitudes toward Greek immigrants. A fascinating article, worth a read.
The bootblack business also led to some of the most unsavory exploitation of Greek by fellow Greek. Owners of shoe shine parlors developed a padrone system that was little more than indentured labor. Passage money was sent to boys in Greece to come and work as bootblacks in America. Once under the control of the padrone, the bootblack might not be paid anything for a year, after which he might earn a salary of twenty dollars a year! (This compared to about ten to fifteen dollars a week for a mill worker in New England.) The working conditions were wretched. The shops opened up at about 6:00 A.M. and closed at 9:00 P.M. on weekdays, and later on weekends. There were no days off. After the doors were closed at night, the boys had to clean the shop and prepare things for the following day.
Unbeknownst to many of the bootblacks, all they had to do in order to escape their situation was simply to walk away from the shoe shine parlor. The padrone tried his best to keep his charges ignorant of this option or at least to overstate the bleakness of alternative employment. He would censor their mail lest complaints crossing the ocean cut into his future supply of bootblacks. After Greek-American newspapers raised their voices against the “flesh peddlers,” some improvement did occur. Yet the fact remained that most of the boys considered their privations worthwhile if they were the only way to get to America. In time, partly as a result of increasing familiarity with American opportunities, partly due to the decline of the shoe shine business, most of the bootblacks found employment in other fields. But for many years bootblacks and Greeks were synonymous in our large urban centers.