WASHINGTON (AP) — The Biden administration proposed Wednesday that future planes produce lower levels of greenhouse gas emissions before they can be certified by federal regulators.

The Federal Aviation Administration proposal would increase fuel-efficiency standards for jets and large turboprop and propeller-driven planes that it has not yet certified, and for planes built after Jan. 1, 2028.

The FAA will develop means to determine the relationship between fuel efficiency and reductions in carbon dioxide emissions.

The rule, if made final, would cover large airliners under development, including Boeing’s 777-X and new versions of its 787 and the Airbus A330neo, plus various business jets and other planes. The FAA said the rule would bring the United States in line with carbon dioxide emission standards set by the United Nation’s aviation organization.

The rule would not cover planes that are already flying.

Planes are a small but growing contributor to greenhouse gas emissions that are tied to climate change. The FAA said civilian planes caused 3% of U.S. emissions before the pandemic.