“The Washington State House Finance Committee made revisions to a proposed income tax after a group of progressive lawmakers said the previous version gave away too much while not doing enough for working families.
“A tax break that would have benefited big businesses has been removed from the latest version of a bill to tax incomes more than $1 million is being advanced by Democratic leaders. A group of 13 progressive lawmakers in the House pushed for those provisions to be stripped.”
"All taxes shall be uniform upon the same class of property within the territorial limits of the authority levying the tax..."
So taxes on things need to be uniform (so, like, 2.5% on ALL property or ALL Doritos).
The voters approved a bracketed state income tax back in the day, but a lawsuit from it basically said "income is property." So they could probably do a flat tax on income, but those are stupid.
But that same article also says "All taxes shall be uniform upon the same class of property within the territorial limits of the authority levying the tax..." and pure value doesn't constitute a different class.
That's basically what I remember backed up by two searches on Google, so sorry if I'm wrong.