SACRAMENTO, Calif.—The chairman of California’s stem-cell agency says he may go to the state’s electorate for an additional $3 billion to bolster their efforts to find cures for debilitating conditions, a spokesman said Nov. 23.

The California Institute for Regenerative Medicine (CIRM) was created in 2004 through voter-approved Proposition 71, which authorized the sale of $3 billion in general obligation bonds to bankroll stem cell research and fund research facilities.

Approved by 59 percent of ballots cast, the California Stem Cell Research and Cures Act of 2004 calls for $295 million to be spent annually, over a 10-year period, to...