Microsoft founder Bill Gates endorsed a Washington state proposal to implement a fee on carbon emissions Tuesday as environmentalists try to build popular support in the state to take action to cut emissions from fossil fuels.

Gates backed the proposal, Initiative 1631, primarily to combat climate change, he said in a blog post.

“Here in Washington state, climate change is on the ballot,” Gates wrote. “If Initiative 1631 passes in November, it will create a fee on emissions that cause climate change, with the goal of boosting the effort to stop the planet from getting disastrously warm.”

While the proposal is technically labeled as a “fee” on carbon, the toll operates similar to a tax and is only classified differently because of unique Washington state rules on what constitutes a tax, according to the nonprofit Tax Foundation. (RELATED: A $240 Per Gallon Gas Tax To Fight Global Warming? New UN Report Suggests Carbon Pricing)