As he seeks to push his controversial vaccine bill through another committee vote Wednesday, Sen. Richard Pan, D-Sacramento, is expected to confront a legion of even more determined opponents than he witnessed last week when Senate Bill 277 cleared its first hurdle.

But this time, adversaries of the bill — which would repeal the state’s personal belief exemption and require that only children who have been immunized for diseases such as measles and whooping cough be admitted to a school in California — are returning with what they say is a powerful trump card.

Parents like San Jose resident Elaine Shtein are being encouraged to bring a son or daughter to stand with them before the eight-member Senate Education Committee on Wednesday with a warning: If the bill passes, they pledge to yank their children out of public and private schools, and home-school them, something they believe will deprive both the state and private school systems of money for every student enrolled.

“This next hearing is going to be a key one for us because of the financial stakes,” said Shtein, 34, who said her 5-year-old son was diagnosed with autism after receiving a vaccine as a baby.

“There will be a lot of other kids there this time to prove a point: No way is anyone injecting something into either of my children without my consent,” Shtein said, adding that she is taking her 7-year-old daughter Sophia up for the day to show her “the democratic process.”

State records show more than 13,000 kindergartners in California are unvaccinated because of either personal or religious beliefs, an analysis by this newspaper revealed. Thousands of other students also lack vaccinations, but state data concentrate on kindergartners as they enter school.

Most public school districts depend on state funding — at least $6,000 per student. However, many school districts in areas with high property values receive relatively little state funding, and actually could financially benefit by drops in enrollment.

“I think pulling students out of school for whatever reason only hurts the students being pulled from class,” said Benjamin Picard, superintendent of the Sunnyvale School District.

“It would not be harmful to schools or the state financially. Such a boycott would not be financially harmful to the Sunnyvale School District,” he said. For his part, Pan, who is a pediatrician, said he plans to employ the same strategy he did last week when the Senate Health Committee passed the bill in a 6-2 vote — despite hundreds of parents and others who turned out to rail against Pan and the legislation.

“When they hear the science and the reason for the bill — that it will protect children — I think they will support the bill,” Pan said afterward.

But opponents say thimerosal, a mercury-containing preservative in some vaccines, is linked to autism, a belief that has been widely discredited by the Centers for Disease Control and multiple scientific studies. However, as a precaution, the Food and Drug Administration in 1999 recommended removing thimerosal from vaccines routinely given to infants.

An informal poll by this newspaper of the eight-person Senate Education Committee, which includes Pan, revealed that three senators are in favor, one is leaning in favor, and three — Republicans Bob Huff and Andy Vidak and Democrat Connie Leyva — are undecided. Only Sen. Loni Hancock, D-Oakland, declined to say.

The bill was introduced in February in the aftermath of the California measles outbreak in December traced to a case in Disneyland, infecting 134 Californians since and dozens more across the country.

Pan and other health experts believe the rising number of parents taking advantage of California’s personal belief exemption that allows them to forgo their children’s vaccines was a factor in the outbreak. In 2000, fewer than 0.77 percent of California kindergartners had vaccination exemptions. By 2014, the rate had more than tripled to 2.5 percent, or 1 in every 40 children.

If passed, SB 277 would allow only medical exemptions for childhood vaccinations, making California the third state in the country, along with Mississippi and West Virginia, to impose that limit.

The legislation also would require schools to notify parents of immunization rates at their children’s schools. But it would not apply to any children attending home-schools, where many protesters said they would educate their children if the bill passes.

Sen. Carol Liu, chair of the Senate Education Committee, is unwavering in her support of the bill.

“This is a basic public health issue. Children should be vaccinated to protect themselves and others,” said Liu, a Democrat who represents La Cañada Flintridge in Los Angeles County.

The California State Parent Teachers Association, which includes 800,000 members, has endorsed the bill. But the California Teachers Association, one of the most powerful unions in the state, on Sunday declined to take a position on the bill.

CTA spokeswoman Claudia Briggs said that the Burlingame-based group’s Council of Education, comprised of about 800 of its more than 300,000 members, voted to take a “watch position” on SB 277.

She said that means the CTA will “monitor the bill and if there are any significant amendments to the bill, those will be brought to the appropriate committees for consideration and possible change of position.”

Asked what kinds of amendments would warrant a change in position, Briggs said she did not know.

Staff writer Sharon Noguchi contributed to this story.Contact Tracy Seipel at tseipel@mercurynews.com or 408 920-5343 and follow her at Twitter.com/taseipel.