Voters across six states will decide nine statewide income or wealth tax measures in this year's midterms—an unusually busy ballot season for tax policy. From 2000 to 2025, voters weighed 40 such measures, a pace of roughly one and a half per year, and the outcomes were evenly split: 20 approved, 20 defeated. This year's slate packs nearly six years of that historical volume into a single election, spanning both taxes on annual earnings and levies on accumulated fortunes.

Much of the attention has centered on California's Proposition 40, a one-time 5% levy on billionaires' net worth designed to help offset federal cuts to health spending. The state's wealthiest residents have poured tens of millions of dollars into defeating it, and Google cofounder Sergey Brin is among those backing Props 41 and 42, which would effectively block Prop 40 if it passes—meaning the billionaire levy's fate could hinge on the countermeasures as much as on its own vote total. But Prop 40 is only one entry on a much longer list.

Notably, lawmakers in these states have not been the ones asking voters to raise taxes on the rich. Most measures that would create or increase such taxes reached the ballot through citizen initiatives crafted by activists and unions.

Growing political willpower

This year, measures to raise taxes on high earners appear in California, Colorado, Washington, Massachusetts, and Cook County, Illinois.

The politics vary by state. California Gov. Gavin Newsom and Democratic gubernatorial candidate Xavier Becerra both oppose Prop 40, even as the California Democratic Party endorsed it; Newsom has since backed Prop 42. In Colorado, Democratic Gov. Jared Polis opposes the proposed graduated income tax, while in Washington, Democratic Gov. Bob Ferguson is leading the defense of the state's new tax.

The states weighing taxes on the rich also account for a large share of corporate America. California hosts 56 Fortune 500 headquarters, followed by Illinois with 29, Massachusetts with 15, Washington with nine, and Colorado with seven. By Forbes's 2023 count, California had 186 billionaires, Illinois 23, Massachusetts 22, Washington 13, and Colorado 12. The ballot fights have already drawn direct involvement from prominent business figures, from Brin in California to the billionaires who funded both sides of Washington's 2010 campaign.

Republican-leaning states are moving in the opposite direction. A North Carolina measure would cut the state's constitutional cap on income tax rates in half, to 3.5%. An Iowa measure would require a two-thirds legislative vote to raise income taxes, and a Utah measure would require 60% voter approval for new or higher taxes. Missouri's Republican-led Senate sent voters a plan to invest state money in the S&P 500 until the returns can replace taxes.

"Over the last few years, we've seen a divergence in state income taxes and taxes on high earners," Jared Walczak of the Tax Foundation told CNBC.

Nearly a 100-year-old fight in Washington

Washington voters rejected income taxes in 10 ballot measures between 1934 and 2010. The final attempt, in 2010, divided the state's richest families: Steve Ballmer and Jeff Bezos each gave $100,000 to oppose it, while Bill Gates Sr. gave $500,000 to support it.

This year, lawmakers passed a millionaires tax themselves after a 25-hour floor debate, and opponents have now placed a measure on the ballot to counteract it. Amazon, Microsoft, and Costco are all headquartered in Washington. Bezos has already sold his Seattle mansion and relocated to Miami, while Ballmer, Gates, and MacKenzie Scott remain among the state's billionaires. If the tax survives, it takes effect in 2028, with the first payments due in April 2029—meaning this year's voters will settle its fate before it collects a single dollar.

A flat tax in Colorado and a surplus in Massachusetts

In Colorado, Amendment 87 would replace the state's 4.4% flat tax with six brackets ranging from 3.7% to 8.4% on income over $1 million. Colorado would become only the third state ever to switch from a flat to a progressive income tax—and it would do so over the objection of its own Democratic governor.

Massachusetts, the second state to make that switch, has collected more than $3 billion from its surtax in the 2025-2026 fiscal year, exceeding projections. Voters will now decide whether those proceeds should count toward the state's revenue limit, a choice that determines whether the surtax revenue sits inside that cap or outside it.

A test run in Cook County

Cook County's question is advisory and would not change any law, but it follows a decision by Illinois House Speaker Emanuel "Chris" Welch to drop a statewide millionaires tax this year after Democrats failed to muster the supermajority needed to put it on the ballot. The state's last attempt, in 2020, failed 55% to 45% after Gov. JB Pritzker spent $56 million supporting it and Citadel's Ken Griffin spent nearly $54 million opposing it. An advisory vote in the county that includes Chicago lets supporters gauge support without risking another statewide loss.

Pritzker is on the ballot again this year, running for reelection, and his race drew an unusual voter. Pope Leo XIV, the Chicago-born pontiff, became the first pope to vote in a U.S. election, mailing in a ballot that includes the governor's race. Pritzker posted, "If the Pope can vote all the way from Vatican City, you can too!" The pope, however, is registered in Will County, so the Cook County question does not appear on his ballot.

This story was originally featured on Fortune.com.