Voters usually decide one or two income or wealth tax measures a year. This midterm season, there are nine

This midterm election features nine statewide measures related to income or wealth taxes, a notable increase from the usual one or two measures per year. The high-profile measures include California's billionaire tax (Prop 40), Colorado's graduated income tax, Washington's new state tax, Massachusetts' surtax, and Cook County, Illinois' advisory question.

Notable opponents include California Governor Gavin Newsom and Democratic gubernatorial candidates, while supporters include California Democratic Party and Democratic governors in Colorado and Washington.

The states involved have a combined total of over 340 Fortune 500 headquarters and more than 60 billionaires. However, Republican-leaning states are moving in the opposite direction, with measures such as North Carolina's plan to cut its income tax rate and Iowa's requirement for a two-thirds legislative vote to raise income taxes.

The debate over taxing the rich has a long history, with Washington voters rejecting income taxes in 10 ballot measures between 1934 and 2010. This year, lawmakers enacted a millionaire's tax, but opponents have put forward a countermeasure that would take effect in 2028. In Colorado, Amendment 87 would replace the flat tax with six progressive brackets, while in Massachusetts, the revenue from its surtax has exceeded projections. Cook County's advisory question gauges support for a potential statewide millionaire's tax.