Libertarian presidential candidate Gary Johnson is supporting a “fee” on carbon dioxide emissions, a policy more closely associated with environmentalists and liberals.

Johnson, formerly a Republican and the governor of New Mexico, told the Juneau Empire that he believes greenhouse gases cause climate change, and a carbon fee could be “a free-market approach to climate change.”

{mosads}“We as human beings want to see carbon emissions reduced significantly,” he told the newspaper, adding that the United States represents a small portion of worldwide emissions, and “I don’t want to do anything that harms jobs.”

Johnson was cautious not to call it a “carbon tax,” the more widely used term for a government levy on carbon dioxide emissions.

A spokesman for Johnson’s campaign clarified Tuesday that the candidate only supports a carbon fee if current regulations on greenhouse gases were repealed.

“Gov. Johnson’s reference to a carbon fee was in the context of the fact that inconsistent, costly, unpredictable and increasing regulations on carbon emissions already constitute a substantial tax,” spokesman Joe Hunter said in a statement.

“However, it is a tax that is not transparent, creates uncertainty in the marketplace, is imposed in the form of higher prices, and may or may not be producing benefits in the form of reduced greenhouse gases.”

He added that “as part of a larger, comprehensive shift from hidden and unpredictable regulatory taxes to a more free market, consumer-driven approach, a transparent and revenue-neutral fee could very well achieve reduced emissions, which Americans clearly desire, more effectively and at less cost to consumers.”

Environmentalists have been pushing for years for government policies to charge polluters for greenhouse gas emissions, either through a carbon tax or cap and trade.

Most Democrats support the proposals, but they are opposed by Republicans and most of the fossil fuel industry, which have labeled a carbon tax as an unnecessary additional cost on energy.

Republican candidate Donald Trump is sharply opposed to a carbon tax, and while Democrat Hillary Clinton hasn’t proposed one, her aides have said she’d be open to discussing the idea.