By Sharon Bernstein, Reuters

A plan to ask voters to repeal a new California law tightening vaccination requirements for school-age children may falter due to a shortfall in signatures needed to put the referendum on the ballot.

The effort is part of a backlash against a bill signed into law this summer by Democratic Gov. Jerry Brown that requires pupils to be vaccinated against childhood diseases unless they have a medical reason to refuse. It was passed after a measles outbreak among unvaccinated people at Disneyland last year.

That law, which goes into effect next year, makes California the third state to eliminate religious and other personal exemptions to vaccinations. It generated strong opposition from some parents, many who feared a now-debunked link between childhood vaccinations and autism and others who feared intrusion on the religious exemption.

Supporters of the referendum had until Monday to turn in 365,880 valid signatures from registered voters in California in order for the measure to appear on the November 2016 ballot.