Washington State Income Tax Signed Into Law — And the Fight to Overturn It Is Already Underway
Washington State is on the verge of enacting its first broad income tax in nearly a century, a development with significant economic implications for the entire Pacific Northwest — including Idaho and Ada County. Governor Bob Ferguson is expected to sign Senate Bill 6346 into law on Monday, March 31, imposing a 9.9% tax on household income exceeding $1 million annually. The legislation passed through the Democratic-controlled Washington State Legislature after months of debate, but opponents are already organizing legal challenges and ballot measure campaigns to overturn it before collections ever begin.
Background: Washington’s Century-Long Resistance to an Income Tax
Washington State has operated without a broad personal income tax for generations, relying instead on a sales tax structure that critics on the left have long labeled regressive. The last time Washington voters approved an income tax was in 1932 — and the state Supreme Court struck it down just one year later in a divided ruling. Voters have rejected income tax proposals repeatedly in the decades since, most recently in 2010.
Supporters of Senate Bill 6346, including labor unions and progressive advocacy groups who rallied at the state Capitol in Olympia in February, argue the new tax corrects a structural inequity by placing a greater burden on the state’s highest earners. They frame it as a necessary fix to a tax system that leans too heavily on lower- and middle-income households through sales taxes on everyday goods.
Opponents, however, see it differently — and they are not standing down. Legal challenges and citizen ballot initiatives are being organized, with specific strategies expected to be announced in the days immediately following the bill’s signing. Given Washington’s constitutional history on this issue, the legal fight could be lengthy and closely watched across the region.
Key Details of the Washington Income Tax Law
Senate Bill 6346 imposes a 9.9% tax rate on household income above $1 million per year. Washington state officials have scheduled revenue collection to begin in 2029, a timeline that gives opponents several years to pursue legal remedies or voter referendums before the first dollar is collected.
The delayed implementation date is notable. It suggests state lawmakers anticipated a protracted legal battle and built in time accordingly. Washington’s constitution has historically been interpreted by courts as prohibiting a graduated income tax, and the state Supreme Court’s 1933 ruling remains a touchstone for opponents who argue this latest attempt faces the same constitutional hurdle.
The bill’s supporters counter that the law is narrowly tailored to affect only the wealthiest households and structured in a way that addresses prior constitutional objections. That argument will almost certainly be tested in court.
Impact on Idaho and Ada County Residents
For Ada County homeowners, business owners, and taxpayers, Washington’s income tax experiment carries real-world significance — even though it takes effect across the border. Idaho has long maintained a comparatively business-friendly tax environment, and the Treasure Valley has already seen significant in-migration from Washington and the broader West Coast over the past several years. High-income earners, entrepreneurs, and business owners looking to reduce their tax liability have been among those making the move to Boise, Meridian, Eagle, Star, and Kuna.
A 9.9% income tax on Washington’s millionaire households could accelerate that trend. Residents and business owners subject to the new tax will be weighing their options, and Idaho — with no such income tax on investment or capital gains at the millionaire threshold — stands to benefit from relocations. That migration brings economic activity, job creation, and increased housing demand, but it also contributes to the population pressures and rising property values that Ada County residents have already been navigating.
The situation in Washington also serves as a timely reminder of the policy choices that make Idaho attractive to families and businesses seeking fiscal predictability and limited government interference in their financial lives.
What Comes Next
Governor Ferguson is expected to sign Senate Bill 6346 on Monday, March 31. Opponents have indicated that legal challenges and ballot measure campaigns will be formally announced in the days immediately following the signing.
Washington voters and advocacy groups opposed to the income tax are expected to pursue a referendum to place the measure before voters, a path that has historically been used to check legislative action in the state. Legal challenges arguing constitutional grounds are also anticipated.
Ada County residents and Idaho business owners interested in tracking this issue should watch for updates from the Washington Policy Center, the Freedom Foundation, and other Pacific Northwest organizations that have been vocal in opposing the legislation. Given the 2029 collection start date, there is time for the situation to change — but the legal and political battles are beginning now.