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New York City closed a preschool program at a yeshiva in Brooklyn on Monday for violating a Health Department order that required it to provide medical and attendance records amid a measles outbreak.

The preschool at United Talmudical Academy, which serves 250 students between the ages of 3 and 5 in the Williamsburg area, is the first program to be closed by the city, as it escalates efforts to stem the country’s largest measles outbreak in decades.

New York City has confirmed 329 measles cases since the outbreak began in the fall, and the cases have largely been confined within the ultra-Orthodox Jewish community. The outbreak began after unvaccinated individuals returned from celebrating Sukkot, a Jewish harvest festival, in Israel.

The closing of the preschool comes as tensions have risen in the ultra-Orthodox community over increased scrutiny and fears of anti-Semitic backlash. On the one hand, most in the ultra-Orthodox community are vaccinated, and the vast majority of prominent rabbis have urged people to vaccinate their children. However, the city’s response to the outbreak has caused vaccine skeptics to double down on their opposition to immunization. The anti-vaccination movement’s well-coordinated and sophisticated messaging campaign, highlighted by magazines, hotlines and conference calls, has convinced some parents that vaccines are dangerous, and that diseases, like measles, are not.