A debate over Washington’s new tax on annual income above $1 million grew contentious Thursday at a Bellevue forum, as Initiative 645 sponsor Brian Heywood challenged Sen. Manka Dhingra over whether the tax could eventually apply to more people. The exchange took place at the Bellevue Chamber’s Eastside Leadership Conference at Meydenbauer Center, less than a month before voters decide the measure on Nov. 3. More than 400 people attended. Initiative 645 asks voters whether to repeal the Legislature’s 9.9% tax on individual income above $1 million. A yes vote would repeal the tax and bar state and local taxes on, or measured by, individual income. A no vote would leave the law in place. Heywood, founder of Let’s Go Washington, and House Minority Leader Drew Stokesbary, a Republican from Auburn, argued that lawmakers could lower the $1 million threshold in the future, making the tax affect more residents. Heywood asked audience members how many believed the threshold would remain at $1 million; few raised their hands. About half said they knew someone leaving Washington. Dhingra, a Democrat from Redmond, defended the tax as a targeted measure intended to make the state’s tax system less regressive. She argued the law applies specifically to the state’s highest earners. Dr. Soleil Boyd, executive director of the Children’s Alliance, said keeping the tax would help sustain funding for child care, education and health care, as well as tax relief for lower-income families. The state’s official fiscal impact statement estimates that Initiative 645 would reduce state revenue by about $11.4 billion from fiscal years 2027 through 2031, affecting money available for K-12 and higher education and human services. The No on 645 campaign says repeal would create a multibillion-dollar budget gap and threaten services and tax relief. Supporters of the initiative counter that the tax is not scheduled to be collected until 2029 and say the measure would prevent it from expanding beyond high earners. Washington Public Disclosure Commission records showed the No on 645 campaign had raised more than $11.5 million as of Thursday. The Washington Education Association contributed $3 million, the Washington Federation of State Employees gave $2.5 million, and the National Education Association contributed $563,764.