Carbon taxes are potentially in play in seven US states, but they are hard to enact.

Legislators in New York, Vermont, Maryland, Massachusetts, Hawaii, Rhode Island and Washington state have been trying to move carbon tax proposals through state legislatures.

A carbon tax proposal in Washington state failed narrowly to advance in the current legislative session that ended in March, despite strong support from the governor and the fact that both houses of the state legislature are under Democratic control.

Carbon tax advocates in Washington are now focused on putting a proposal to impose carbon taxes, called Initiative 1631, on the November ballot. They need 259,622 voter signatures by July 6 to do so.

Under the proposal, a tax would be imposed on fossil fuels sold or used in the state and electricity generated or imported into the state. The tax would be paid only by large emitters. It would start at $15 per metric ton of carbon content starting in 2020 and increase by $2 a year plus inflation. The tax rate would keep increasing until the state reaches its 2035 greenhouse reduction target and state emissions are on a trajectory that makes it likely a separate 2050 target will be reached no later than 2050.

Several sectors would be exempted from the tax. For example, the tax would not apply to fuel for agricultural use or to coal used in a large coal-fired power plant that is already scheduled to be shut down in 2025.

Electric utilities would be receive an offsetting credit if they pursue clean energy investment plans. 

An earlier ballot initiative to impose such a tax failed in 2016, but a broader coalition is backing the initiative this year. Many environmental groups opposed the 2016 ballot initiative over disagreements about how the money collected would be spent. The new proposal is 38 pages.