Although Bill Gates, Sr. made headlines in spring with contributions totaling a half-million dollars to Initiative 1098, the leading backer of the income-tax measure is now a union of service-industry employees. One of the country's most powerful labor groups, the SEIU has given $735,000 (from national, state, and local affiliates) since the campaign began, according to the latest filings with the Washington State Public Disclosure Commission.

Last week, the SEIU state council gave $215,000, records show, and local SEIU affiliates gave another $100,000. Meanwhile, the local UFCW, which represents grocery and other workers, gave $75,000. State employee groups have contributed $200,000 to the campaign so far. Union money is nearly half of the $2.3 million raised for I-1098.

The measure on this year's ballot would create—for the first time in state history—an income tax; it would apply to people earning more than $200,000 a year. The revenue would be dedicated exclusively to education and health care.

The Defeat 1098 campaign has raised $1.5 million, with its leading contributor, Joseph Barer, giving $100,000.

You can search all the initiative filings over here.