The Washington state Senate has approved a landmark bill to impose a personal income tax on the state’s highest earners, advancing a proposal that would mark the first statewide income tax in Washington’s history.

In a 27-22 party-line vote on Monday, lawmakers passed legislation that would levy a 9.9 percent tax on annual personal income above $1 million, sending the measure to the state House for further consideration in the current 60-day legislative session.

Under Senate Bill 6346, the new tax would apply beginning in 2028 and primarily targets households with income exceeding $1 million per year.

Backers argue the measure would help address the state’s long-term general fund shortfall, support investment in public education, health care and social services, and rebalance a tax system they say disproportionately relies on sales and property taxes that weigh more heavily on low- and middle-income households.

Most Senate Democrats supported the measure, while all Republicans opposed it, warning that the introduction of a personal income tax could undermine the state’s longstanding tax climate and have broader economic implications.

Three Democratic senators — Adrian Cortes, Drew Hansen and Deborah Krishnadasan — joined Republicans in opposing the bill, underscoring divisions within the majority caucus.

The proposal now moves to the state House of Representatives, where legislators have until the March 12 adjournment to debate and potentially amend the bill.

Supporters are also discussing possible additions, including tax relief provisions for working families and small businesses, as they seek to build broader support.

Washington is one of only a few U.S. states without a personal income tax, a distinction many voters have protected for decades.

Previous attempts to introduce income taxation have repeatedly failed at the ballot box or in the legislature, and constitutional provisions and voter initiatives have historically limited lawmakers’ ability to impose such levies without substantial legislative majorities or public approval.

Advocates of the new tax say it would generate billions of dollars in annual revenue once implemented, potentially easing budget pressures and allowing for targeted tax cuts and public spending priorities.

Gov. Bob Ferguson has signaled his support for an income tax on high earners if it is paired with measures to increase tax credits for working families and provide relief for small businesses, though legal challenges and possible voter referendums remain likely if the bill becomes law.