United Airlines Inc. extended its suspension of flights to and from Hong Kong, citing new coronavirus testing protocols for crew arriving in the Asian financial hub, while American Airlines Group Inc. also canceled plans to resume services from Dallas/Fort Worth.

Hong Kong updated its Covid-19 prevention and control measures this week, requiring all air-crew members arriving at the city’s airport starting Wednesday to provide throat saliva samples at a government facility nearby.

“UA877 was canceled due to recent changes in testing protocol at HKG, and United flights to and from HKG are suspended through July 10 westbound and their corresponding returns,” United said in a statement referring to its flight due to depart San Francisco on Wednesday. HKG is the Asian city’s airport code.

“We are currently assessing how this impacts our future operations,” the airline said.

American’s Flight 125 due to depart Dallas/Fort Worth on Thursday also was canceled, according to its website.

American has extended its suspension of flights to Hong Kong until Aug. 5 as it “works with the appropriate authorities to address the concerns regarding the testing mandate,” said Patrick O’Rourke, vice president of the Allied Pilots Association, a union representing the carrier’s pilots.

The union expressed concern that anyone who tested positive in Hong Kong would be admitted to a hospital as soon as possible and anyone refusing to undergo a test would be subject to a fine and imprisonment.

“Upon learning of these new testing requirements, APA immediately contacted management to discuss the situation and raise concerns, both contractual and other, about the new testing requirements,” O’Rourke said in a statement.

The United and American flights were due to be both airlines’ first commercial passenger operations to the city since they suspended services in early February.

Hong Kong has become a focal point of increasingly frayed relations between the U.S. and China as Beijing moves ahead with national security legislation over the city, prompting the Trump administration to declare that Hong Kong no longer is sufficiently autonomous.

Hong Kong has reported an increase in coronavirus cases following an almost three-week lull, with the government warning that the city might be in the early days of a wider outbreak. Hong Kong has reported a total of 1,323 cases and seven deaths, while U.S. infections and deaths stand at 3.1 million and more than 132,000, respectively.