A New York City suburb has banned children who aren’t vaccinated against measles from schools, markets and other public spaces, amidst one of the worst U.S. outbreaks in decades of the sometimes-fatal disease. Rockland County Executive Ed Day said the ban will target parents who refuse to give their children the MMR vaccine against measles, mumps and rubella.

Ed Day: “Effective at the stroke of midnight tonight, March 27th, anyone who is under 18 years of age and is unvaccinated against the measles will be barred from public places until the declaration expires in 30 days or until they receive at least their first shot of MMR.”

The order will affect an estimated 6,000 unvaccinated children and their families. The outbreak, which has seen at least 150 people infected with measles since last October, has mostly been confined to Rockland County’s Orthodox Jewish community, which has particularly low vaccination rates.