Americans for Prosperity Florida (AFP-FL), the conservative/libertarian group funded by the Koch brothers, is trashing a carbon tax bill put forward by U.S. Rep. Carlos Curbelo that Curbelo says would help combat climate change.

The Republican broke from his party to offer up the legislation. His bill, the “MARKET CHOICE Act,” would repeal federal taxes on certain fuels and replace them with a carbon tax.

“I truly believe that one day this bill, or legislation similar to it, will become law,” Curbelo said in comments reported by Reuters.

“It will spark an important debate about investing in our country’s infrastructure, the way we tax and what to do to protect the environment.”

But a spokesperson from AFP-FL said the bill would result in a tax increase that Americans shouldn’t stand for.

“Rep. Curbelo’s tax hike proposal would resurrect bad ideas and produce even worse alternatives,” said Chris Hudson, state director of AFP-FL.

“A carbon tax paired with a border adjustment tax would mean higher prices for essentials like gasoline, electricity, food, and clothing—and those price hikes would hit the least fortunate hardest.”

Hudson called for members of Congress to vote against Curbelo’s legislation.

“With the current strong economic outlook, we should seek ways to empower consumers, get out of control Washington spending in check, and build on the promise of the historic tax reform Congress passed late last year. The ‘MARKET CHOICE Act’ would be a harmful proposal that should be swiftly rejected by members of Congress.”

The group has long pushed back against tax increases, particularly those tied to efforts to tackle climate issues.

AFP-FL pointed to a 2013 Congressional Budget Office report, which noted, “The costs of a carbon tax would not be evenly distributed among U.S. households. For example, the additional costs from higher prices would consume a greater share of income for low-income households than for higher-income households, because low-income households generally spend a larger percentage of their income on emission-intensive goods.”

Nevertheless, Curbelo argues his bill would help curb the effects of climate change. That’s an issue he’s long been passionate about, often in conflict with other Republicans.

Curbelo’s seat in Florida’s 26th Congressional District could be at risk in 2018. If he gets past a primary challenge, by Souraya Faas, he will then take on the winner of the Democratic primary between Debbie Mucarsel-Powell and Demetries Grimes.

Analysts currently rate the CD 26 race as a toss-up.