The LATAM unit had already adjusted flight itineraries through April 25, but extended the changes after workers on Friday rejected a salary package proposed by the company. The strike had been on for 12 days as of Sunday.

"We are very aware that our passengers are the most affected by this paralysis, so we are making all efforts to mitigate the impact," Claudia Sender, vice president for customers at LATAM Airlines Group, said in a statement.

Under the previous itinerary adjustments, 1,575 flights were cancelled, affecting more than 273,000 passengers. It was not immediately clear how many would be affected by the extension.

The company said it would keep negotiating to "reach a satisfactory agreement with the union as soon as possible."

LATAM was created in 2012 through a merger of Chile's LAN and Brazil's TAM. The company, headquartered in Santiago, has operating units in Argentina, Brazil, Chile, Colombia, Ecuador, Paraguay and Peru.

(Reporting by Antonio De la Jara; Writing by Hugh Bronstein; Editing Daniel Wallis)