Vaccine critic: Robert F Kennedy Jr spoke at a documentary screening in Sacramento, California on Tuesday. The son of the late Attorney General Robert Kennedy is a vaccine critic and is currently trying to stop a bill in the state that would make childhood immunizations mandatory

Robert F Kennedy Jr sparked controversy Tuesday when he compared childhood vaccinations to a holocaust.

At a screening of the documentary Trace Amounts, the nephew of President John F Kennedy spoke out against a proposed bill in California which would make childhood immunizations mandatory - no matter what their parent's personal beliefs on the vaccines.

The documentary purports that there is a connection between thimerosal - a chemical found in several childhood vaccines - and a rise in autism among American children - despite the majority of the scientific community dismissing any connection.

'They can put anything they want in that vaccine and they have no accountability for it,' Kennedy said of the Centers for Disease Control and Prevention at the Crest Theater stage in Sacramento.

'They get the shot, that night they have a fever of a hundred and three, they go to sleep, and three months later their brain is gone. This is a holocaust, what this is doing to our country,' Kennedy added.

Kennedy said that the documentary helped convince lawmakers in Oregon stop a similar measure in that state, and was hoping it would have a similar effect in California.

Anti-vaccine advocates delivered free tickets to the screening to every California lawmaker on Monday, and cordoned off three rows in the theater for them on Tuesday that remained empty.

Unpopular opinion: The film screened on Tuesday purports that there is a connection between the vaccine chemical thimerosal and autism, though it is a theory the scientific community has mostly dismissed

Advocate: Kennedy speaks with audience members at the Crest Theater in Sacramento on Tuesday

Senate Bill 277 was scheduled to have its first hearing Wednesday in front of the Senate Health Committee. If passed, the law will remove an exemption in the vaccination law that currently allows parents to cite personal beliefs in not vaccinating their children.

The anti-vaccination movement has been sweeping the country, and with more parents refusing common immunizations, many long-dormant illnesses like measles and whooping cough are breaking out in schools.

Senator Richard Pan, a Democrat from Sacramento and a pediatrician, called Kennedy's endorsement of the anti-vaccine cause as dangerous.