Microsoft co-founder Bill Gates supports the income-tax initiative and will vote for it, according to the I-1098 campaign.

Sandeep Kaushik, a spokesman for Yes on 1098, said Gates' father, Bill Gates Sr., had a long conversation with his son on the matter and confirmed his support for the ballot measure.

Gates Sr. helped draft the income-tax initiative and is the public face for the measure, appearing in a recent television commercial for the campaign.

This is the latest in a string of announcements since Monday showing where some of the richest and most powerful people in the state are lining up on the measure, which would create a 5 percent tax rate on annual income exceeding $200,000 for individuals and $400,000 for couples, and a 9 percent tax rate on income that tops $500,000 for individuals and $1 million for couples.

Initiative 1098 also would cut the state portion of property taxes by 20 percent and newly exempt 118,000 businesses from the state business and occupation (B&O) tax.

On Monday, the Defeat 1098 campaign noted that Microsoft CEO Steve Ballmer and Amazon.com founder and CEO Jeff Bezos have lined up against I-1098. Ballmer and Bezos each has contributed $100,000 to the Defeat 1098 campaign.

More than $7 million total has been raised by both sides in the initiative fight.

The Defeat 1098 campaign has raised about $3.5 million, with a little more than $1 million of that last week.

The Yes on 1098 campaign has raised about $3.6 million. Major individual contributions to that side include $200,000 from Ann Wyckoff, the granddaughter of William Pigott, founder of local truck-manufacturer Paccar; $250,000 from Nicolas "Nick" Hanauer, a partner at venture-capital firm Second Avenue Partners; and $500,000 from Gates Sr., a prominent Seattle lawyer.

But much of the campaign's money has come from labor groups, including about $1.2 million from the Service Employees International Union and $100,000 each from the Washington Education Association and the Washington Federation of State Employees.