Some people who spoke to Eyewitness news said mandatory vaccinations is a good idea, while others said the choice should be up to the parents.
California State Sen. Richard Pan, a pediatrician, is one of the people behind Senate Bill 277.
"We can't have people fearing to go outside, to go to their school, to go to a store, to get on public transport, to go to a theme park because they're afraid of catching a disease like measles," he said.
Eyewitness News asked for an interview with the "No on 277" campaign, but did not hear back.
The bill must go through several committees before it can even receive a vote.