SEATTLE – Philanthropists Bill and Melinda Gates have together donated $1 million to the I-1631 Carbon Tax Fund that would charge a fee on carbon emissions from fossil fuels.

Gates wrote in a blog post last week that he would contribute to the Yes on 1631 campaign but he didn’t reveal how much.

New campaign finance records show that he and his wife have each donated $500,000 in support of the initiative. The measure has raised a total of $11 million.

Opponents including top oil companies have raised nearly $22 million to defeat it. They say it would hike gas and electricity costs and exempts too many big polluters.

(The Associated Press contributed to this story)