CHICAGO — United Airlines plans to order a fleet of 100-seat jetliners from either Bombardier or Embraer if it can agree on terms for a two-year contract extension with pilots in expedited bargaining.

Reaching a deal would assure labor peace with a crucial union for new Chief Executive Officer Oscar Munoz and bring back some flying now done by regional partners with cramped, less-efficient 50-seat planes. For Bombardier or Embraer, a sale to United would be a significant victory as they try to place their biggest narrow-body models at the largest U.S. carriers.

"This time of senior leadership change is a unique opportunity for us," United Senior Vice President Douglas McKeen wrote in an Oct. 2 letter to union chief Jay Heppner, in a reference to Munoz's hiring last month after the ouster of predecessor Jeff Smisek. McKeen proposed capping the talks at 45 days.

An airline spokeswoman, Megan McCarthy, confirmed the overture but declined to discuss the possible negotiating terms at the unit of United Continental Holdings. Dave Kelly, a spokesman for United's chapter of the Air Line Pilots Association, said: "We cannot discuss offers or proposals."

Buying new 100-seat planes for mainline flying would be a lure for pilots, because it would generate jobs and appeal to their interest in cutting-edge aircraft — an affinity jokingly referred to in the industry as "shiny jet syndrome."

Bombardier and Embraer are both mentioned in a clause in United's current contract: Taking their largest new narrow-body airliners, the CSeries and E2, would allow United to also add more larger regional planes in 2016 to replace the 50-seaters. McKeen wrote that any contract extension "will also include a firm order" of new, small narrow-bodies. He didn't identify a manufacturer.

Messages left for Bombardier and Embraer spokeswomen were not immediately returned.

United has struggled to reach unified labor agreements since the 2010 merger between former United parent UAL Corp. and Continental Airlines. Flight attendants, for example, still work under contracts for the predecessor companies. Pilots have such an accord, so an extension would let Munoz's team focus on trying to reach breakthroughs with attendants and mechanics.

The pilot talks carry high stakes for Bombardier, which is seeking to end an order drought dating to September 2014 for its marquee CSeries aircraft. The CSeries has been shut out among major carriers in North America, the world's largest aviation market, while Embraer has made inroads.

Offering a pay raise and a sleek new aircraft is not unusual, but the gambit does not guarantee success. In July, Delta Air Lines abandoned plans to add $4 billion of Boeing and Embraer jets after pilots rejected an expedited contract proposal.