The U.S. government suspended 44 scheduled flights from the U.S. to China by that nation’s airlines in response to restrictions placed on American carriers over COVID-19 testing protocols.

The U.S. Department of Transportation today issued restrictions against four Chinese airlines in a dispute that has been percolating since the pandemic erupted in 2020. China in recent months had suspended flights on Delta Air Lines Inc., American Airlines Group Inc. and United Airlines Holdings Inc. citing an effort to block COVID-19 transmission, something U.S. authorities say is a violation of a treaty on flight access.

The action by the U.S. government is the latest sign of tensions between the two nations over issues ranging from trade policy to alleged spying. The DOT said its goal has been to reduce tensions over travel rules, but it was forced to take action in response to recent moves by China.

The Civil Aviation Authority of China’s actions against the three carriers “are adverse to the public interest and warrant proportionate remedial action by the department,” the U.S. agency said in the order.

The order restricts flights by Air China Ltd., China Eastern Airlines Corp., China Southern Airlines Co. Ltd. and Xiamen Airlines Co. Ltd. The four Chinese airlines didn’t immediately respond to requests for comment outside of normal business hours in that country.

Under China’s strict rules to limit the spread of the coronavirus, airlines are penalized with flight suspensions if passengers arriving from other nations test positive for COVID-19. The DOT documented 44 flights by U.S. carriers that were suspended by China after passengers had tested positive since Dec. 19.

The Chinese government clears each passenger to travel to that country and the U.S. airlines followed all of the requirements, the DOT said. The U.S. airlines should not be penalized when travelers test positive after arriving in China, the DOT said.

China’s requirements for how aircraft are cleaned and quarantine requirements for foreign airline crews have also created tension.

The recent actions by the two governments are a setback to getting the U.S.-China flights — which tend to be more lucrative and were a growing market — back to normal in the wake of the pandemic. Flights between the two nations were halted completely in early 2020.

“We are supportive of the actions taken by the Department of Transportation to ensure the fair treatment of U.S. airlines in the Chinese market,” said Airlines for America, a trade group representing large carriers.