The Washington state constitution doesn’t allow a graduated income tax to be imposed. About 80 years of case law make that clear.

Yet, 15 state lawmakers plowed ahead this week with an effort seeking the state Supreme Court to reverse precedent and allow the city of Seattle to impose a local graduated income tax. The senators and representatives, all Democrats from the Puget Sound region, filed a brief with the high court on Monday.

This effort, like previous efforts to allow Seattle to impose a tax on the wealthy, is not just about allowing the state’s largest city to impose its own income tax. It’s an end run around the constitution’s prohibition on income tax so that state lawmakers and other cities could impose one at some point.

It’s an affront to good government and the state’s citizens, who have voted 10 times since 1960 to not allow an income tax. Six of those votes were specifically rejections of amending the state constitution.

If these 15 lawmakers want the opportunity to impose an income tax in cities or across the state, the option is to seek a seventh change to the state constitution.

Of course, it’s highly likely — as in close to certain — that such an effort would be strongly rejected once again by voters.

Income tax has long been the third rail in Washington state politics. It’s been seen as untouchable because the public has shown zero appetite and much contempt for imposing an income tax to go along with sales tax.

When it’s been proposed to lower sales tax in favor of an income tax, voters have been skeptical. Many fear, and with good reason, that the final tab would be more than is currently paid.

That’s not to say our current tax system, which is heavily reliant on sales tax, is great. It is not. Sales tax is regressive, meaning those with lower incomes pay a higher percentage of their earnings than those who are wealthy.

Tax reform is needed, but that’s not on the agenda right now.

The voters in Seattle might have softened to an income tax in recent years, but based on the recent statewide approval of Initiative 976 — the imposition of $30 car tabs and a reduction in transportation taxes and fees — Washingtonians are not in the mood for higher taxes or fees.

This effort to circumvent the constitution should end with a rejection by the state Supreme Court.

Again, the only way to change the state constitution is by amending it through a supermajority vote of the Legislature and approval at the ballot box by the people.