Rockland County, which is about 40 miles north of New York City, said on Tuesday that children under 18 years of age who haven’t been vaccinated against the measles cannot attend any public places with 10 or more people. The move was announced alongside county executive Ed Day declaring a county-wide State of Emergency over an increasingly concerning measles outbreak.

“This is an opportunity for everyone in our community to do the right thing for their neighbors and come together,” Day said in a statement. “We must do everything in our power to end this outbreak and protect the health of those who cannot be vaccinated for medical reasons and that of children too young to be vaccinated.”

Rockland County has been hit especially hard by a measles outbreak affecting children across the U.S. The county, which is about 40 miles north of New York City, has so far confirmed 153 cases of measles in children under 18 years of age. Most of those children haven’t been vaccinated.

Measles has been well-contained over the years, thanks to the MMR vaccine, which protects children against measles, mumps, and rubella. Children usually get their first dose of the vaccine before they’re a year old and subsequent treatments when they get older. It’s been an effective protection against measles for decades.

However, in recent years, an increasing number of parents have decided against vaccinating their children as anti-vaccination literature has proliferated online, professing the vaccinations could create bigger health issues. In turn, maladies those vaccinations are meant to prevent have made a comeback and infected children.

Rockland law enforcement will not be patrolling or requesting vaccination records from children. The county did say, however, that those in violation of the mandate could face charges from the Rockland District Attorney’s office.

“We will not sit idly by while children in our community are at risk,” Day said. “This is a public health crisis, and it is time to sound the alarm, to ensure that everyone takes proper action to protect themselves and their neighbors; for the health and safety of all of us in Rockland.”