Parents who do not want to have their children vaccinated will now need a medical professional's signature before enrolling them in school.
It is one of more than 100 bills Gov. Jerry Brown signed on Sunday.
The law will force parents who opt out of the vaccination to go to the doctor and learn about their options and the risks they are taking.
In the past, parents who did not want their children to be vaccinated could simply sign a waiver themselves. Now however, they must have a medical professional sign the waiver in order for it to be valid.
Gov. Brown has directed the State Dept. of Public Health to oversee the new policy to ensure that it does not overburden California parents. The bill also allows for certain religious exemptions.
The new requirement will go into effect on Jan. 1, 2014.