The Seattle City Council voted 9-0 Monday to pass a citywide income tax on high earners.
The 2.25-percent tax applies to annual income over $250,000 for an individual and $500,000 for a couple filing jointly.
Mayor Ed Murray supports the tax and is expected to sign it into law.
The tax is scheduled to apply to income earned in 2018, though proponents say they expect a lawsuit that may delay its implementation.
Legal experts view the city's legislation as a test case that may determine whether citywide income taxes are legal in Washington state.