Union pilots at Frontier Airlines have asked federal authorities to take steps to release them from negotiations on a new contract, a request that, if granted, could lead to the first major U.S. airline strike in eight years.

In a letter dated Friday, the Air Line Pilots Association told the National Mediation Board, which governs airline industry labor relations, that the two sides were at an impasse, with little hope of reaching an agreement during ongoing mediation sessions. The pilot union accused airline management of “an approach that is inconsistent with good-faith bargaining.”

Strikes are rare at U.S. airlines because federal regulations make them difficult. Though Frontier’s pilots overwhelmingly authorized a strike last August, they can only legally walk off the job if federal regulators allow it. In this case, if the National Mediation Board agrees the sides are at an impasse, it would ask the union and the airline to settle the contract in binding arbitration. If one side declines arbitration, pilots could strike, though they would have to wait out 30 days before doing so. During that “cooling off period,” pilots and management might be more likely to reach a deal because stakes would be higher.

Almost always issues get worked out, which is why there hasn’t been a major pilot strike since Spirit Airlines pilots struck in 2010, after they were released from negotiations. The strike lasted less than a week, but it worked — pilots got their new contract, with wage increases, after the airline was forced to stop flying.

It’s not clear whether it will come to that at Frontier. In a statement, a Frontier spokesman said the two sides continue to talk, suggesting the airline doesn’t agree the sides are at an impasse. “We continue to be actively engaged in negotiations with our pilots for a new contract and continue to exchange proposals under the guidance of the National Mediation Board,” Frontier’s Richard Oliver said.

The National Mediation Board couldn’t be reached for comment late Monday.

There are, however, considerable similarities between Spirit, circa 2010, and today’s Frontier. In 2010, Spirit had recently become the first ultra-low-cost-carrier in the United States, and it was controlled by Indigo Partners, a private equity firm, which was preparing it for an initial public offering. In 2013, Indigo sold its stock in Spirit and bought Frontier.

Indigo quickly turned Frontier into a discount airline like Spirit, slashing costs, adding fees, and lowering fares. About a year ago, once it had costs that roughly matched Spirit’s, Frontier announced plans for its own IPO. But it was delayed a few months later, and no longer appears imminent.

At Frontier, Indigo inherited a management-friendly contract, because pilots had made concessions in 2008, just a couple of months after Frontier filed for bankruptcy according to the pilot union.

Now, the union said, Frontier’s 1,200 pilots are the lowest-paid narrow-body pilots in the United States, and captains make 40 percent less than the industry average.

“Despite its industry-leading financial performance, Frontier Airlines has insisted upon a substantially-discounted pilot contract,” the union said in its letter to the National Mediation Board.

In the letter, the union suggested fear of a strike might make management more serious negotiators. “It’s clear that an agreement will only be reached with the added urgency of a 30-day cooling off period,” the union said.