"My child, my choice!" they shouted on Thursday.
They came with signs and bullhorns, many of them parents with children in tow.
"It removes parental choice. A lot of people try to paint us as being anti-vax. But we're not anti-vax. We're pro-choice," said Dennis Hupka of Holmdel, N.J.
The bill they're protesting - if it becomes law - would eliminate religious exemptions for vaccinations in school children in New Jersey.
Medical exemptions would have to be authorized by a doctor or advance practice nurse, and those exemptions could be subject to review by local and county boards of health.
Assemblyman Herb Conaway of Burlington County, who is also a physician, co-sponsored the bill. He says while he believes in freedom of religion, he says that shouldn't apply to vaccines.
"I also think it's inappropriate for religion to be involved in the medical decision of whether or not to do vaccines. I think it's a question of science," said Conaway.
He and other advocates of the bill say the benefits of vaccines far outweigh the risks.
Last year, 19 people in New Jersey were diagnosed with measles, according to the state department of health.
"We've seen less and less people vaccinated and the drop in those vaccination rates has led to the return of measles on our continent," said Conaway.
The protests continued throughout the day on Thursday, each demonstrator with their own reason. Some say vaccines have harmed their child. Some say this denies them religious freedom.
The bill passed through the state assembly last month.
It is now in the hands of the state Senate, which could take a vote on the bill next week.