The BJ&B factory in the Dominican Republic makes caps for Nike and Reebok and for colleges like Penn State and the University of North Carolina.
The factory, north of the capital, Santo Domingo and employing 1,600 people, has been a major focus for US students' campaigns against sweatshop labour. It is probably the largest factory among the free-trade zones of the Caribbean, Central America or Mexico to have been unionised.
The new union has now negotiated a contract that provides pay rises, scholarships and other benefits that are unheard of among the Dominican Republic's 500 foreign-owned plants. The agreement, signed at the start of April, is the latest victory for the US-based coalition of anti-sweatshop student groups and union activists.
"I never thought a group of students, thousands of them, could put so much pressure on these brands," said Ignacio Hernandez, the general secretary of the Federation of Free Trade Zone Unions. "We were determined to win, but without them it would have taken us five more years."
Workers tried to form a union about six years ago because managers were forcing them to work overtime. Some workers complained that supervisors would insult workers or threaten to hit them. Union leaders said the average wage for workers was about $31 a week.
United Students Against Sweatshops sent thousands of letters to the factory, and also sent a student volunteer for most of last year to help the union organise.
Scott Nova of the Worker Rights Consortium said, "We eventually persuaded [the bosses] to produce a public letter signed by managers pledging neutrality, no intimidation and that the workers had the right to make their own choice [to join the union or not]." Even after the union won a majority the factory began layoffs that singled out union members. Rehiring those workers - about 10 of whom remain unemployed - became one of the first points of the contract talks, which began earlier this year.