SACRAMENTO, Calif. — Gov. Gavin Newsom is seeking last-minute changes to one of the most controversial bills facing California lawmakers, a measure designed to crack down on doctors who sell fraudulent medical exemptions for vaccinations.

The measure would allow state public health officials to investigate doctors who grant more than five medical exemptions in a year and schools with vaccination rates of less than 95%.

Newsom spokesman Nathan Click said Wednesday that changes are needed to make the rules clear.

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The governor is seeking amendments making it clear that enforcement will start next year. They would also remove a requirement that doctors swear under penalty of perjury that they are not charging fees to fill out medical exemption forms.

Bill author Sen. Richard Pan says he hasn't recently discussed changes with the governor.