The Washington State House of Representatives has approved a proposal to introduce a nine point nine percent tax on the highest earners, advancing a plan supporters say would reshape the state’s tax system while drawing strong criticism from business groups.

The measure, often referred to as a “millionaires tax,” would apply to personal income above one million dollars.

Lawmakers backing the proposal argue that the new levy would generate billions of dollars in additional revenue to support education, healthcare, childcare and other public services.

The bill passed after an intense and prolonged legislative debate that stretched for more than a full day, reflecting the deep political divisions surrounding the plan.

Several members of the Democratic majority joined Republican lawmakers in opposing the measure, highlighting unease even within the party advancing the legislation.

Washington is one of the few states in the United States that does not currently impose a broad personal income tax, relying heavily on sales taxes and business levies instead.

Supporters of the proposal say the new tax would make the system more balanced by placing a greater share of the burden on the wealthiest residents.

Business organisations and economic groups reacted sharply to the vote, warning that the policy could fundamentally change the state’s business environment.

Some leaders described the proposal as a “seismic shift” that could discourage investment, drive high-earning residents to relocate and weaken the state’s reputation as a technology and innovation hub.

Opponents also raised legal concerns, noting that Washington courts have historically interpreted the state constitution in ways that limit income taxation.

Legal challenges are widely expected if the measure ultimately becomes law.

Supporters in the legislature countered that the state faces long-term funding pressures and that targeting the highest incomes is the most equitable way to address them.

They argue that only a small share of residents would be affected while the revenue could strengthen essential public programs.

The legislation now moves forward in the state’s legislative process, where additional approval steps remain before it could be enacted and potentially face court scrutiny.

The vote represents one of the most significant tax policy debates in Washington in decades and signals a broader national conversation about how states should fund public services while balancing economic competitiveness and fairness.