Forty-three states tax personal income, according to the nonprofit Tax Foundation. Eight have a flat tax and the others have some form of progressive taxation. California’s rate tops out at 13.3 percent for income above $1 million, the highest in the country and the result of a 2012 ballot measure to erase a budget gap by increasing sales taxes and levies on income above $250,000.

The higher income taxes were supposed to expire after seven years and the sales taxes after four. A union-backed coalition has gathered signatures toward a November ballot measure that would extend the higher income taxes for 12 years, while allowing the sales tax increase to expire.

"The wealthiest are already paying the tax," said Jennifer Wonnacott, a spokeswoman for the coalition pushing the California Children’s Education and Health Care Protection Act of 2016. "The need to extend those rates for the wealthiest taxpayers is still very real."

Jon Coupal, president of the Howard Jarvis Taxpayers Association, named for the sponsor of a 1978 ballot measure to limit property-tax increases, said he understands the politics of higher taxes on the wealthy, rather than on property or sales. Still, Coupal said raising income taxes would cause many business owners and entrepreneurs to leave California for states such as Nevada, which has no income tax.

"Nothing is more mobile than rich people and capital," Coupal said. "If you keep piling taxes on top of other taxes, you’ll see people leave."

A Stanford University study in 2014 said evidence of millionaires fleeing is "hard to find." In a telephone interview, Kim Rueben, a senior fellow in the Urban-Brookings Tax Policy Center in Washington, said higher taxes on their own rarely spur people to move, noting that most increases are relatively modest. Tax rates, she said, are one factor among many that influence where the rich live and do business.
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Los Angeles County, whose 10 million residents compose a quarter of California’s population, last week requested a change to state law that would allow it to levy a local income tax to augment services for the homeless.

Colorado activists need more than 98,000 signatures by August to put on the November ballot a measure that would add an additional 0.5 percent levy on income of more than $405,000 to the state’s current 4.63 percent flat tax. Minnesota’s legislature is considering a ballot measure to fund long-term care for senior citizens and the disabled by extending Social Security taxes to higher wages. Maine voters will decide the fate of a 3 percent surcharge on income exceeding $200,000 per year, with proceeds earmarked for public schools.

Supporters of a Massachusetts tax increase are aiming for a 2018 ballot measure to expand the current 5.1 percent flat tax by 4 percentage points on income exceeding $1 million. Massachusetts has a convoluted history with the income tax: Measures to replace the flat tax with a graduated rate have been defeated at the ballot five times, while two proposals to eliminate the tax altogether also failed.

The national interest in income inequality, combined with Congress’ unwillingness to raise the federal rate, could make the difference in 2018, said Chuck Collins, the great-grandson of 19th-century meatpacking baron Oscar F. Mayer and a proponent of the Massachusetts initiative.