The airline has had to cancel hundreds of flights recently due to increased pilot maintenance reports and sick leave usage.

American Airlines, a unit of AMR Corp that filed for bankruptcy in November, began implementing cost cuts for its pilots this month after a U.S. bankruptcy judge ruled the airline could abandon its collective bargaining agreement with the pilots union.

"We do not want to pursue a legal remedy, but we will be left with little alternative if Allied Pilots Association APA.L does not take action to stop those pilots who are intentionally harming the operation," the company said in the letter.

The union representing pilots at American Airlines said last week that it had called for no job action at the bankrupt carrier.

"American's operations have continued to suffer for more than a week now, and we must take the appropriate steps to ensure our customers and our airline are protected," a company spokesman said in statement.

The pilots' union was not immediately available for comment Thursday. (Reporting by Bijoy Koyitty in Bangalore; Editing by Supriya Kurane)

• A Permanent Economic Emergency