Will Washington’s “Millionaire Tax” Survive a Court Challenge?
Washington Democrats’ “millionaire tax” proposal (SB 6346) is designed to sound simple: 9.9% on personal income over $1 million.
The legal problem is also simple: Washington courts have treated an income tax as a property tax for nearly a century. And Washington’s Constitution makes property taxes hard to do in a progressive way.
The constitutional speed bump: “Income = property”
In Washington, the key precedent is Culliton v. Chase (1933). The Washington Supreme Court held that income is “property” under Article VII of the Washington Constitution.
That classification matters because property taxes must be uniform within the same class of property. A tax that applies only above a threshold (or uses brackets) is the opposite of uniform.
SB 6346 is explicitly non-uniform: 0% up to $1 million; 9.9% above $1 million. That looks like the exact kind of structure Washington courts have struck down when the tax is characterized as a tax on income/property.
The uniformity problem (and why this will be litigated immediately)
Washington’s Constitution requires taxes to be uniform on the same class of property. If income is property, then a “tax only on high earners” becomes legally vulnerable because it taxes the same kind of property (income dollars) differently depending on who owns it and how much they have.
This is why opponents keep calling these proposals unconstitutional “income taxes,” even if the bill is drafted with careful terminology.
“But didn’t the Supreme Court uphold the capital gains tax?”
Yes — in Quinn v. State (2023) the Washington Supreme Court upheld the state capital gains tax.
But that decision does not green-light a general income tax. The Court upheld the capital gains tax by characterizing it as an excise tax on the transaction (the sale/exchange of assets), not a tax on income itself.
SB 6346 is different: it taxes aggregate annual income above $1 million, not a specific transaction. That difference is likely to be the heart of the court challenge.
Seattle already tried a “high earner” income tax — and lost
Seattle’s attempt at a high-earner income tax was invalidated in Kunath v. City of Seattle (Wash. Ct. App. 2019), largely on the same “income-as-property / uniformity” framework. The state Supreme Court let that decision stand.
SB 6346 will be challenged in the same lane.
Bottom line
If SB 6346 becomes law, the core question won’t be politics — it will be constitutional taxonomy:
- Is this a tax on income (and therefore “property”)?
- Or can the state plausibly frame it as an excise tied to a specific taxable incident?
Under current Washington precedent, SB 6346 looks like a direct income tax with a non-uniform rate structure, which is exactly the combination that has historically failed in Washington courts.
