Court Battle Begins Over Washington State's New 9.9% High-Income Tax

Opponents challenge the constitutionality of the controversial new law in court

Apr. 9, 2026 at 5:57pm

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A photorealistic painting of the exterior of a grand, classical stone courthouse building with tall columns and arched windows, the facade bathed in warm, golden sunlight with deep shadows, conveying a sense of civic gravitas and judicial authority.The upcoming legal battle over Washington's new high-income tax law will ultimately be decided by the state's highest court.Olympia Today

Opponents of Washington's new 9.9% income tax on households earning over $1 million plan to formally launch their legal challenge to the law's constitutionality on Thursday. Led by former state Attorney General Rob McKenna and former state Supreme Court Justice Phil Talmadge, the plaintiffs will argue the tax violates the state constitution's requirement for uniform property taxes.

Why it matters

Washington has long resisted implementing a state income tax, with voters rejecting proposals multiple times. This new high-income tax law represents a major shift, and the outcome of the legal battle could determine whether the state can move forward with a more progressive tax system.

The details

The lawsuit will be filed by the Citizen Action Defense Fund, with McKenna and Talmadge expected to lead the litigation. They will argue that the state Supreme Court has consistently ruled that income is considered property, and therefore any tax on income must be applied uniformly as required by the state constitution. The backers of the tax law, including Senate Majority Leader Jamie Pedersen, believe the law is legally sound and expect it to ultimately be upheld by the state's Supreme Court, even if lower courts initially rule against it.

  • The lawsuit is scheduled to be formally launched at a 10 a.m. news conference on Thursday, April 9, 2026.
  • The new 9.9% income tax law took effect immediately after being signed by Governor Bob Ferguson on March 30, 2026.
  • Collections under the new tax law are expected to begin in 2029 and generate around $3 billion per year.

The players

Rob McKenna

Former Attorney General of Washington state and expected to lead the legal challenge against the new income tax law.

Phil Talmadge

Former Justice of the Washington State Supreme Court and expected to lead the legal challenge against the new income tax law.

Jackson Maynard

Executive Director of the Citizen Action Defense Fund, the organization filing the lawsuit against the new income tax law.

Jamie Pedersen

Washington State Senate Majority Leader and a lead sponsor of the new 9.9% income tax law.

Bob Ferguson

Governor of Washington who signed the new 9.9% income tax law into effect.

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What they’re saying

“It's great. We will now have that robust argument.”

— Jamie Pedersen, Washington State Senate Majority Leader

“Washington's constitution is clear, and the courts have been equally clear for nearly a century — income is property, and progressive income taxes are unconstitutional under existing law.”

— Rob McKenna, Former Washington State Attorney General

What’s next

The superior court judge who is assigned the case is expected to initially rule the new income tax law is unconstitutional, but the ultimate decision will be made by the Washington State Supreme Court.

The takeaway

This legal battle over Washington's new high-income tax law represents a major test of the state's tax system and its ability to implement more progressive taxation. The outcome could have significant implications for the future of taxation in Washington.