New York (CNN Business) Three of the largest US airlines -- Delta, American and United -- have canceled more flights between the United States and China because of concerns about the spread of coronavirus.

For American Airlines, the nation's largest carrier, the decision comes after the union representing 15,000 pilots sued the company Thursday to immediately halt its US-China service, citing "serious, and in many ways still unknown, health threats posed by the coronavirus."

American AAL moved up its planned suspension of flights between the United States and mainland China beginning Friday. It had originally announced that flights between Los Angeles and Shanghai and Los Angeles and Beijing would be suspended from February 9. Its Hong Kong flights will continue to operate.

"Based on the U.S. Department of State's recent increase of the China Travel Advisory to a Level 4 (Do Not Travel), American is suspending its operations to and from the Chinese mainland beginning today through March 27," American said in a statement.

The union applauded the move. "Now that American is ceasing operations in China, the ultimate goal is that all our passengers and crew will remain safe and that was our main goal," Captain Dennis Tajer, a spokesperson for the Allied Pilots Association, told CNN Business.