The union representing American Airlines’ pilots has filed suit in Dallas against the company in an effort to immediately halt all scheduled flights between the U.S. and China and directed all crewmembers to decline any assignments between the two countries. The Allied Pilot Association issued a statement Thursday citing “serious, and in many ways still unknown, health threats posed by the coronavirus.” American Airlines has already suspended two routes—between Los Angeles and Shanghai and Los Angeles and Beijing—from between February 9 and March 27.

The APA’s lawsuit notes that American Airlines currently operates approximately 56 monthly flights between Dallas/Fort Worth International Airport and airports in China and that each American Airlines crewmember working a trip to China must remain on the ground for approximately 32 hours between flights to comply with federal rest regulations. In its filing, APA cites warnings issued by the United States Centers for Disease Control and Prevention and other health organizations discouraging all “nonessential travel” to China.

“The safety and well-being of our crews and passengers must always be our highest priority—first, last, and always,” said APA President Capt. Eric Ferguson. “Numerous other major carriers that serve China, including British Airways, Air Canada, and Lufthansa, have chosen to suspend service to that country out of an abundance of caution. The APA leadership has asked American Airlines management to follow suit, but to date they have not canceled any U.S.-China flights. We are therefore compelled to seek injunctive relief.”

American’s announcement on Wednesday to cut service to China due to the new coronavirus outbreak followed a similar move on Tuesday by United Airlines, which canceled 24 round trips from February 1 to 8. Delta Air Lines late Wednesday joined its two U.S. competitors in reducing service to China, slashing half its frequencies—from 42 to 21—from February 6 through April 30.