(Reuters) – Pilots at airline Avianca are refusing to work overtime hours amid a labor dispute, their unions said on Monday, a decision only affecting pilots employed through the company’s Colombian operations.

avianca-jetThe company controlled by Avianca Holdings, which also controls El Salvador’s Taca, said in a statement that it has offered to raise pilots’ salaries and offered other benefits. However, it said the employees have refused to discuss it and have still to present their demands to the company.

Avianca said it has taken measures necessary to minimize the impact of the dispute on its operations.

Avianca pilots refused to work overtime on at least one previous occasion to pressure the company to respond to its demands, causing delays to its flights.