A California vaccination bill (State Bill 277) that has generated intense debates pitting personal rights against public health stalled in the state Senate Wednesday, with lawmakers saying it could unconstitutionally deprive unvaccinated children of an adequate education by barring them from schools.

The measure would have prevented parents from seeking vaccine exemptions for their children because of religious or personal beliefs, making California the largest of only three states with such strict requirements. Thirty-one states currently have no personal belief exemption; only Mississippi and West Virginia do not have a religious exemption.

Supporters plan to bring back the proposal next week revising it to address the concern raised in the Senate Education Committee, but it wasn't immediately clear how the bill might change.

The proposal was among several drafted across the nation in the wake of a measles outbreak that started at Disneyland in December, sickening more than 100 people in the U.S. and Mexico.

It's generated such an angry debate that the proposal's author, Sen. Richard Pan, a Democratic pediatrician from Sacramento, has received added security. In addition to threatening messages sent to his office, opponents of the legislation have posted images online comparing Pan to Adolf Hitler.

Hundreds of people lined the Capitol halls ahead of the Wednesday morning committee hearing, with about 600 opponents outnumbering roughly 100 supporters, a crowd far larger than normal for even the most contentious measures.

It was the second hearing after the Senate Health Committee approved the measure 6-2 last week.

Parents have been on both sides of the issue, with some calling the vaccination plan an unconstitutional government overreach and others saying it was necessary to save lives.

Carl Krawitt, of Corte Madre near San Francisco, told lawmakers Wednesday that he feared for his 6-year-old son's life during the measles outbreak because the boy, Rhett, could not bevaccinated while he was treated for leukemia. Krawitt said his family has already bore the financial and emotional toll of a child with cancer.

"We're here for the community," Krawitt said. He added, "You have a duty to legislate from solid evidence, not from fear, and keep our schools safe."

Opposing parents have told lawmakers that since vaccines come with risks, they should have the choice of whether their children should get such shots. Many said they would rather homeschool their children than comply with a vaccination requirement.

Among the risks, opponents say, vaccine drugs have been linked to autism and other developmental diseases, even as the medical community says such claims have been disproved.

Robert Moxley, an attorney from Wyoming who represents families who say they've been injured by vaccines, testified that the bill violates freedom of choice. He told lawmakers that the proposal would not stand up in a court challenge.

"It seems to me this is a solution in search of a nonexistent problem," Moxley said.

Under the bill, medical waivers would continue to be available for children with certain health problems. Unvaccinated children would have to be home schooled.