HONG KONG (AP) — China’s biggest state-owned air carriers have hit back at a U.S. proposal to bar them from flying over Russia when traveling to or from the U.S.

The U.S. side has said such flights give Chinese airlines an unfair cost advantage over American carriers, which cannot cross through Russian airspace. Moscow closed Russian airspace to U.S. air carriers and most European airlines in 2022 in response to Western sanctions for Russia’s invasion of Ukraine.

Air China, China Eastern and China Southern are among six Chinese airlines filing complaints over the order proposed last week to prohibit such flights by Chinese carriers.

China Eastern said in its filing this week to the U.S. Department of Transport that the proposed ban would “harm the public interest" and "inconvenience travelers” from both China and the U.S. The additional flight time would result in higher costs and elevated air fares, which increases the burden on all travelers, it said.

China Southern warned that a Russian airspace ban would adversely affect thousands of travelers. Air China said it estimates at least 4,400 passengers would be affected if the ban takes effect during the Thanksgiving and Christmas season.

Last week, China’s foreign ministry spokesperson Guo Jiakun also hit back at the proposed ban, saying the move would be “punishing” passengers around the world.

David Yu, an aviation industry expert at New York University Shanghai, said that U.S. carriers' inability to fly over Russian airspace has increased flight paths for some U.S.-China routes by roughly two to three hours. Longer journeys require more fuel and pressure U.S. carriers’ profitability.

“The U.S.-China route historically has been a money-maker for airlines on both sides,” Yu said. “From the Chinese carriers’ perspective, if you can go through Russia, your costs go down.”

Despite that, Chinese carriers have struggled with losses, especially since the COVID-19 pandemic.

The U.S. Department of Transportation said in its proposed order that Chinese carriers' ability to cross Russian airspace has caused “competitive imbalances” between American and Chinese airlines.

“Being able to use the most efficient route provides a competitive advantage because it usually results in the shortest flight time duration, thereby offering a more appealing option to travelers,” the department said last week.

The U.S. Department of Transportation said it would consider public comments before finalizing the plan.

European airlines including Air France-KLM have also complained.

In a filing to the Department of Transportation, United Airlines urged that Hong Kong’s flagship carrier Cathay Pacific, which is not included in the list of Chinese airlines, also be subject to the ban.