Former WA AG argues proposed income tax is illegal

Rob McKenna cites state constitution and court rulings in legal memo against millionaire tax

Published on Feb. 20, 2026

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Former Washington State Attorney General Rob McKenna has issued a legal memo arguing that a proposed tax on personal income over $1 million is unconstitutional. McKenna cites the state constitution's 14th Amendment, approved by voters in the 1930s, which defines 'property' broadly and has been interpreted by the state Supreme Court to include income. He argues this makes a graduated income tax illegal under current law.

Why it matters

The proposed millionaire income tax has been a contentious political issue in Washington state, with supporters arguing it's a fair way to have the wealthy contribute more, while opponents say it violates the state constitution. McKenna's legal memo provides ammunition for those opposed to the tax, potentially complicating efforts to pass it.

The details

McKenna's memo argues the proposed 9.9% tax on personal income over $1 million, or combined household income of more than $1 million, is unconstitutional based on the 14th Amendment to the state constitution. That amendment, approved by voters in the 1930s, defines 'property' broadly and has been interpreted by the state Supreme Court to include income. McKenna cites a 1933 court ruling that declared 'income' is property and a tax on income is a tax on property.

  • The state Senate voted 27-22 in favor of the proposed millionaire income tax on Monday.
  • In 2022, the state Legislature passed a capital gains income tax, which the state Supreme Court ultimately declared to be an excise tax.

The players

Rob McKenna

Former Washington State Attorney General and Republican who represented plaintiffs in a lawsuit against the state's capital gains income tax.

Senate Bill 6346

The proposed legislation that would impose a 9.9% tax on personal income over $1 million or combined household income of more than $1 million.

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What they’re saying

“The purpose of Amendment 14 was to expand the reach of property taxes to intangible forms of property, including stocks, bonds, and money, which had previously evaded taxation.”

— Rob McKenna, Former Washington State Attorney General (dailyfly.com)

“No more positive, precise, and compelling language could have been used than was used in those words of our Fourteenth Amendment. It needs no technical construction to tell what those words mean. The overwhelming weight of judicial authority is that 'income' is property and a tax upon income is a tax upon property.”

— Culliton v. Chase, 1933 State Supreme Court Ruling (dailyfly.com)

What’s next

The state Supreme Court will likely have to rule on the constitutionality of any income tax legislation passed by the state Legislature.

The takeaway

This legal memo from a former state Attorney General provides a strong argument against the proposed millionaire income tax, potentially complicating efforts to pass it and setting up a likely court battle over the issue of whether an income tax violates the state constitution.