The U.S. says it is considering imposing tariffs, in response to an international proposal to charge ships for their carbon dioxide emissions in order to help fight climate change. 

Reuters reported on September 4 that the U.S. had threatened to impose tariffs, visa restrictions and port levies against nations that supported proposed new rules from the UN’s International Maritime Organization, shipping’s global regulator; rules that aim to slash the industry’s future greenhouse gas emissions.

“We are actively exploring and preparing to act on remedies including tariffs, visa restrictions, and/or port levies should this effort succeed,” a U.S. State Department spokesperson said in an email. “We will fight hard to protect the American people and their economic interests.”

The U.S. had previously criticized the proposed framework and labeled it a “global carbon tax,” according to an August statement. The emissions rules still need to pass the potentially significant hurdle of adoption at the IMO, scheduled for October.