Delta Air Lines and its pilots union have requested mediation after failing to negotiate a new contract in their talks so far.
It's the first time in 15 years that Delta and its pilots union have turned to mediation.
The company and the Air Line Pilots Association union at Delta had agreed to file for mediation with the National Mediation Board if they did not reach a deal by March 31.
Delta's pilots union several months ago re-opened negotiations with a proposal for a nearly 40 percent raise over three years. As Delta reports billions of dollars in profits, pilots say they want to recover from past pay cuts levied during the airline’s bankruptcy and financial challenges in the past decade.
The proposal came after both sides reached an agreement last year, and rank-and-file pilots voted to reject that proposed contract over pay and other issues.
In a letter to pilots, Delta's senior vice president of flight operations Steve Dickson wrote that the company "remains committed to reaching an industry-leading agreement that reflects the Delta pilots' significant contributions to our continued success. I hope we can do so in a reasonable timeframe."
But he also wrote: "To be successful and maintain our momentum over the long term. we must take a balanced approach that is sustainable in both good times and bad."
The pilots union said since their contract became amendable Dec. 31, 2015, "progress has been slow."
John Malone, chairman of the Delta pilots union's master executive council, told pilots the goal is to complete an agreement by this summer.
Malone wrote in a letter earlier this month to pilots: "The market for pilots is rising, and delay will only cost Delta more."
He also told pilots that the union's leadership has named a strike committee chairman -- a step taken by unions to bolster their negotiating position.