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 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.

Delta said Friday it was suspending all flights from the United States to China from February 6 until April 30. The airline said it’s continuing routes until February 5 to “ensure customers looking to exit China have options to do so.” It said that it will “continue to monitor the situation closely” and adjust its schedule accordingly.

Affected customers can request a refund, rebook their flight after the suspension lifts or speak with an agent for other options. Delta (DAL) currently operates 42 weekly flights between the United States and China, including daily service connecting Beijing and Detroit and Seattle, and Shanghai and Atlanta, Detroit, Los Angeles and Seattle.

United Airlines also said Friday it was suspending flights from is US hub cities and Beijing, Chengdu and Shanghai from February 6 to March 28. Until next week, the carrier will “operate select flights to help ensure our US-based employees, as well as customers, have options to return home,” it said in a statement.

On Tuesday, United said it was suspending operations to Hong Kong because of a drop in demand. Operations will be suspended Feb. 8-Feb. 20, the airline said.

“Our last flights will depart San Francisco on February 5 (flight 877 and flight 869) and the last returning flight will depart Hong Kong on February 7 (flight 862),” the airline said in a statement on its website.

The coronavirus, a potentially fatal respiratory disease, first emerged in Wuhan, China in early December and has since spread across China and appeared in some other countries, including the United States, Japan and India. The World Health Organization has declared the coronavirus epidemic a public health emergency of international concern.

Fears over the spread of the disease has forced both US and global carriers to amend their schedules as demand for China travel declines.

British Airways, Air Asia, Cathay Pacific, Air India, IndiGo, Lufthansa and Finnair have announced plans this week to slash the number of flights they are operating to China or stop flying to the country entirely. Other airlines are offering customers refunds.

Shannon Liao contributed to this report