A bill in California to ban religious and personal exemptions from vaccinations has sparked a bitter controversy. Above, a vial of measles, mumps and rubella vaccine and an information sheet is seen at Boston Children's Hospital in Boston, Massachusetts, Feb. 26, 2015. Reuters/Brian Snyder

A bill in California that would curb options for parents who want to avoid vaccinating their children is facing one of the harshest public backlashes in recent legislative history. The controversy is so bitter that its author, a physician whom critics have compared to Adolf Hitler, has been provided with extra security.

The proposal, Senate Bill 277, would prevent parents from obtaining waivers that would allow them not to vaccinate their children on religious or personal grounds. Instead, it would grant exemptions only for medical reasons. The bill has passed the Senate Health Committee and was slated to be discussed by the Senate Education Committee on Wednesday.

Supporters of the bill consider it vital for public health, particularly after a measles outbreak earlier this year affected more than 100 people throughout the United States. The origin of the outbreak was traced to Disneyland in Anaheim, California. The state has more than two-dozen counties with vaccination rates below 92 to 94 percent among kindergartners, which is considered the critical level for achieving herd immunity.

Democratic state Sen. Richard Pan, a pediatrician and the author of the bill, has been placed under added security after online images compared him with Hitler. Meanwhile, more people have called Democratic state Sen. Carol Liu over the vaccine bill than any other proposal, including those regarding immigration and physician-assisted suicide, a spokesman for Liu told the Associated Press.

Hundreds demonstrated in Sacramento, the state's capital, to oppose the bill last week after it passed the Senate Health Committee. Some parents who oppose vaccination claim that vaccines have been linked to autism, even though the scientific article that originally made that claim has since been discredited. Others oppose the idea of government-mandated vaccination.

If the bill becomes law, parents who oppose the measure have threatened to withdraw their children from public and private schools and home-school them instead. California would join just two other states, Mississippi and Virginia, with such strict requirements for vaccines.