Lawmakers in New York have voted to eliminate religious exemptions for school vaccines for children, as the state grapples with a measles outbreak.
The law passed on Thursday night, and led to chaotic scenes in the statehouse as anti-vaccination supporters clashed with lawmakers.
Much of New York's outbreak has centred around orthodox Jewish communities.
More than 1,000 Americans have been diagnosed with measles in 2019. Health officials say the disease is resurging.
Last month, the US Centers for Disease Control and Prevention (CDC) warned that the US, which effectively eliminated measles in 2000, may lose its "measles elimination status" as infections climb to a 27-year high.
The new law in New York, which was passed by the state's Democratic Senate and Assembly chambers, bans parents from claiming religious exemptions which used to allow their children to forgo vaccinations that are normally required for school.
"I'm not aware of anything in the Torah, the Bible, the Koran or anything else that suggests you should not get vaccinated," said Bronx Democrat Jeffrey Dinowitz, who sponsored the bill.
State Senator Brad Hoylman added: "We're putting science ahead of misinformation about vaccines and standing up for the rights of immuno-compromised children and adults, pregnant women and infants who can't be vaccinated through no fault of their own."
Governor Andrew Cuomo, who signed the bill into law only hours after it was passed by lawmakers, said in a statement: "The science is crystal clear: Vaccines are safe, effective and the best way to keep our children safe."
"While I understand and respect freedom of religion, our first job is to protect the public health and by signing this measure into law, we will help prevent further transmissions and stop this outbreak right in its tracks."
Nearly three quarters of New York's measles cases have occurred among orthodox Jews in the Williamsburg neighbourhood of Brooklyn in New York City.
California, Mississippi, West Virginia and Maine have also banned non-medical vaccine exemptions for school children.
Similar exemptions are still allowed in the other 45 states, but lawmakers in some have begun efforts to remove them.
As the law was passed in Albany, religious protestors who had gathered to voice opposition to the bill began chanting "shame", while others screamed profanity.
"We'll be back for you Jeffrey!" shouted one man in religious garb, addressing the bill's sponsor.
"I'm sure the hallways are very dangerous for me right now," Mr Dinowitz responded in a comment to the New York Post after the apparent threat.
The law allow students 30 days after they enter school show proof of their immunisation. Without such proof, students may be prevented from enroling.
Two schools in Williamsburg were shut down on Thursday by health officials, after inspections revealed that they have been allowing unvaccinated students to attend classes.
The closure marks eleven schools that have been shut after the New York City mayor issued an order requiring vaccinations for anyone who attends, works for, or visits a school in the Brooklyn neighbourhood.
Until the US immunisation campaign began in the 1960s, thousands of children were sickened by the sometimes fatal disease every year.
Cases dropped to as few at 100 per year a decade ago, according to CDC figures.