Southwest Airlines pilots’ union plans to hold a vote that could give it the power to call a potential strike, a move that comes weeks after the carrier’s holiday meltdown further strained ties with its workers’ unions.

Even if Southwest’s pilots vote in favor of giving the union authority to call a strike, it wouldn’t be immediate and it would require permissions from the federal National Mediation Board.

Southwest and the Southwest Airlines Pilots Association have been in negotiations for a new contract for years.

Union leaders have focused on better work rules and scheduling for Southwest workers. During the travel chaos last month, many pilots and flight attendants were stranded and had to wait on hold to reach schedulers or hotel services.

The union’s president, Casey Murray, said it was the first time the union has held a strike authorization vote.

“This decision is not one based on emotion, but I would be lying if I said that I wasn’t angry,” Murray wrote to pilots. He said the union is also negotiating “gratitude pay to compensate our Pilots who suffered through the meltdown.”

The strike vote will begin May 1, Murray said. Scheduling it for then means “we can best prepare for and give our customers time to book elsewhere so that they may have confidence in their summer vacations, honeymoons, and family outings,” he wrote to members.

Southwest Airlines didn’t immediately respond to a request for comment.

Delta Air Lines pilots voted in October in favor of allowing the union to authorize a strike, though the union and company about a month later reached a preliminary deal for a new contract.

Labor negotiations are underway across the U.S. airline industry, with unions seeking higher pay and better working conditions after carriers’ attempt to quickly ramp up flying capacity strained staff and crews.

Southwest reports quarterly results on Jan. 26, and executives are likely to face questions from analysts about potential labor deals and the impact of the thousands of holiday cancellations. The carrier has said the incident could have cost it more than $800 million.