A labor union is an organization that develops where a workforce who have a common trade or work at the same establishment band together in order to take advantage of the increased power of collective bargaining. Through the united voice of a labor union, its members can collectively seek benefits and concessions from employers that would likely be unavailable if any individual employee attempted to negotiate the terms of employment on his or her own. This is because the union can collectively withhold its labor ("strike") in the event that its members are dissatisfied with their working conditions. The resulting loss of income and deprivation of needed goods and services often brings employers back to the bargaining table.
Chief Miles O'Brien proudly claimed that his ancestor, Sean Aloysius O'Brien, led his union into the eleven-month Anthracite strike of 1902, before being killed one week before the strike's end. His body was found in the Allegheny River, riddled with bullets. (DS9: "Bar Association")
The formation of a labor union is forbidden and severely punished in Ferengi society. (DS9: "Bar Association")
Rom formed a union in late 2372, after Quark became even more ruthless to his staff. Brunt and the Ferengi Commerce Authority became aware of it and took steps to destroy it. Quark later gave all of his staff an increase in wages. (DS9: "Bar Association")
Rom cited the union as having no effect on Ferengi attitudes to him, although his brother caustically told him "they didn't want anything to do with you before you formed the union..." (DS9: "Body Parts")
In 2374, Quark shouted at two idle Ferengi waiters, saying "What is this, a union meeting?" (DS9: "Resurrection")