DENVER—In a historic first, more than 250 Frontier Airlines pilots picketed their airline’s corporate headquarters Wednesday to protest their stalled negotiations with management and the Frontier owners’ decision to enrich themselves instead of investing in the airline.

The pilots, who are represented by the Air Line Pilots Association, Int’l (ALPA), are demanding that the airline negotiate in good faith to raise pilot wages, a promise Frontier made when the pilots sacrificed millions in salary and benefits to help the airline avoid bankruptcy in 2011.

“Despite our pilots’ enormous sacrifice and the indications showing that Frontier Airlines is now extremely profitable and rewarding its investors, Frontier pilots are still the lowest-paid Airbus pilots in the country,” said Capt. Tracy Smith, chairman of ALPA’s Frontier pilot group. “The loan that Frontier pilots gave to our company is past due—we want industry-appropriate pay and benefits like our fellow pilots at other airlines.”

Frontier’s 1,100 pilots have been in negotiations with the company for a new contract since March 2016 and have been in federal mediation under the guidance of the National Mediation Board (NMB) for more than six months. The two sides are still far apart on economic issues.

“The company’s conduct at the bargaining table is getting worse—not better. It refuses to settle the most minor issues that we raise, refuses to agree to even small economic improvements, and continues to delay in any way it can,” Capt. Smith said. “We want the company to begin bargaining in good faith and have asked the NMB to intervene more forcefully to move negotiations forward.”

On March 31, the privately held company filed documents with federal regulators as part of its plans to take the airline public and begin selling stock later this year. The newly released financials reveal that the airline is extremely profitable and has channeled hundreds of millions of dollars in profits to its investors while shortchanging employees and aggressively cutting operational costs.

That lack of investment in infrastructure has led to repeated operational meltdowns at the airline, and Capt. Smith warned that the problems are going to get worse, especially if pilots begin leaving the airline to seek better opportunities in a pilot friendly hiring market.

“By the end of 2017, Frontier will have paid its investors hundreds of millions of dollars over the past two years. It’s time to stop looting the airline, invest in the airline’s future, and share Frontier’s profits with the employees who have contributed so much to its success,” he said.

Joining the pilots as a show of solidarity was Capt. Tim Canoll, ALPA’s president.

“The Frontier pilots have the full support of their national union in their fight for a fair contract that reflects their sacrifice and contribution to their company’s current success,” said Capt. Canoll. “All ALPA members stand shoulder-to-shoulder with the Frontier pilots.”