From the mid-nineteenth century onward, the garment industry experienced rapid growth. Von Drehle writes, "By the turn of the century, more New York immigrants worked in clothing factories than in any other business, and the industry was doubling in size every decade."

At the time, the average workweek was eighty-four hours. This era also saw the rise of sweatshops, where newly arrived immigrant workers were required to work “more and more hours for less and less pay” in squalid conditions, often tiny rooms in tenement buildings. The shirtwaist, a type of woman's blouse, became the fashion sensation of the 1890s, and the combination of the shirt with a long skirt symbolized women's liberation.

The Triangle Shirtwaist Company was the largest blouse-making operation in New York at the time, shipping out approximately two thousand garments a day. Russian immigrants Max Blanck and Isaac Harris established the company in 1900, and operations greatly expanded over the next decade. In 1902 they moved to a modern factory on the ninth floor of 27 Washington Place, also known as the Asch Building, which was thirty times the size of a typical tenement workshop. By 1909 they had taken over the eighth and tenth floors. The eighth floor was "at least one floor higher than the fire department could easily reach," and the lack of regulation during this time meant that there were no sprinklers installed or fire drills practiced.

Blanck and Harris, who had previously been factory workers themselves, constantly worried about the growing unrest and adopted a number of tactics to suppress protests. One of these was an "inside contractor" system, which gave space on the assembly line to contractors who in turn hired machine operators to fill the chairs themselves. This system required a lump sum payment from Blanck and Harris but allowed the contractor to give their workers as much or as little money as they saw fit. However, contractors often sympathized more with the workers than the owners, and in 1908 a contractor named Jacob Kline demanded more money after struggling to cover his expenses and pay his workers. After being forcibly removed, the workers walked out in solidarity, but the strike died down, and everyone returned to work the following Monday. The Triangle owners established an in-house union, the Triangle Employees Benevolent Association, in an attempt to appear supportive of their workers, but the officers were all relatives of Blanck and Harris, and they continued to fire anyone who tried to cause trouble.

A year after the incident with Kline, Triangle workers finally went on strike amid widespread unrest and with Clara Lemlich's encouragement. In late September 1909, Triangle workers were shut out of the factory and told that they would be fired if they were found to be organizing with a union other than the one set up by Blanck and Harris. Some employees had attended a secret organizational meeting earlier that week; when they refused to apologize, Blanck and Harris posted advertisements seeking new employees, and in response, the remaining workers went on strike. The Triangle owners attempted to break up the protests by hiring female sex workers to lead the group of new recruits through the striking employees. Women on the picket line began pleading with the new workers to join their strike, and police intervened when the sex workers began to attack. However, it was striking workers who were arrested, and throughout the strike the police took the side of the owners and worked to protect their interests. Blanck and Harris sent thugs after key figures such as strike chairman Joe Zeinfield, hoping this would force the strikers to back down.

Approximately a month into the strikes, the Women's Trade Union League decided to start sending well-to-do progressives to the picket line, believing that the public would find the suffering of women—and particularly middle-class women—more compelling. The key confrontation occurred when WTUL president Mary Dreier visited the picket line as the factory's new employees left. One of the Triangle managers called her a "dirty liar" when she was trying to convince a worker to join the strike. Dreier was arrested after demanding a police officer protect her, and the arrest appeared on the front page of mainstream newspapers the next day. This came just two days after the November elections, when Tammany Hall had "lost every important municipal office below the mayor's." Upon seeing the papers, Charles Murphy ordered the police to treat the striking workers with greater moderation, as young progressive women being dragged to jail was not an image with which he wanted Tammany to be associated.

Meanwhile, momentum was building toward a general strike. Blanck and Harris began preparing their fellow factory owners for this possibility, and twenty leading shirtwaist manufacturers formed the Employers Mutual Protection Association at an emergency meeting. The factory owners publicly vowed to never accept the shirtwaist union, sending a private letter to fellow shirtwaist manufacturers encouraging them to do the same. For Blanck and Harris, along with other employers, their primary goal was to resist the newly formed International Ladies Garment Workers Union (ILGWU) and enforce a closed shop system, meaning workers could only join in-house unions.