A Colombian pilots union voted in favor of a strike at Avianca Holdings SA, which the company argues is illegal. The ACDAC union says that its members include about 700 pilots that work for the company and won’t fly during the strike—slightly more than half of Avianca’s pilots. Avianca said Colombian laws forbid those offering essential services from striking, and it will take disciplinary action if it starts, according to an emailed statement. The strike may start as soon as Sept. 20 and last for as long as 60 days, the union said. Labor negotiations were called off this week after 20 days of talks that failed to reach an agreement, with the union alleging “grave discrimination” of Colombian pilots relative to other regions. “It’s not Avianca’s call to judge the strike, that’s up to the Transport Ministry,” union president Jaime Hernandez, said during a news conference Friday. “We regret that passengers and their travel plans will be affected .” Avianca said it had made over 20 proposals to increase benefits for Colombian pilots during the negotiations, before the pilots “unilaterally ended” the talks. Earlier this year, the airline reached an agreement with the another association that represents about half of its pilots, but it hasn’t been able to reach an agreement with ACDAC since 2013.