As Mullany was undoubtedly aware, there was resistance to the idea of a female union from all classes of men. Society took a dim view of women working at all, and working-class men generally believed that women employees would depreciate the value, and the wages, of their own labor. Undaunted, Mullany drew inspiration from the local Iron Molders International Union, and gained their cooperation and support. She organized her fellow laundresses, about 300 of them, and during the frigid month of February in 1864, she and her co-worker Esther Keegan led a weeklong strike that resulted in a 25-percent wage increase and improved working conditions. After the success of the first strike, the ad-hoc organization doubled in membership and became the Troy Collar Laundry Union.
A second strike brought wages to $14 a week. Mullany and her family built a three-story, brick, double-row house with her increased wages. They lived in one apartment and rented out the others.
In his closing speech, Sylvis described Mullany as “one of the smartest and most energetic women in America."
In 1868, she traveled to New York City to attend the National Labor Congress at Germania Hall. Among the other three representatives from New York was Susan B. Anthony, who would later write about Mullany’s union activities. Kate was praised by delegates for her determination, organizational abilities, and her humanitarian efforts on behalf of her fellow unionists. On the last day of the congress, President William Sylvis appointed her as Assistant Secretary—making her the first woman to be named to a national labor union office. Chief among her tasks was the coordination of national efforts to form workingwomen’s associations, a duty she was dedicated to for many years.
In his closing speech, Sylvis described Mullany as “one of the smartest and most energetic women in America, and from the great work she has already done, I think it not unlikely that we may in the future have delegates representing 300,000 working women.”
But captains of industry were not easily thwarted in their drive for ever-larger profit margins, and the invention of paper collars put an end to the gains in the laundry trade. The Troy Collar Laundry Union was dissolved in 1870. Susan B. Anthony wrote sympathetically about the union and Mullany’s “working women’s ventures,” even though Mullany was not interested in politics and declined to join the mostly middle-class suffragist movement. Instead, she and her union officers started a cooperative laundry and a cooperative collar-and-cuffs factory. But these initiatives failed under the relentless pressure and bullying tactics of local factory owners, who collaborated in preventing the cooperatives from getting work.