The agreement with U.S. supplier LIFT by EnCore marks a shift in Boeing's longtime practice of requiring airlines to make seat purchases from suppliers before they are actually shipped to the plane maker.
Analysts and investors said Boeing's move underscored its frustration with the failure of some major suppliers to deliver seats on time, which can snarl aircraft production.
Airbus made a similar move last year, partnering with German seat maker Recaro to offer a "seller-furnished-equipment" seat for the Airbus A320 family.
Boeing's purchases from LIFT might be small initially but investors and analysts saw growth potential. The industry spends about $4.6 billion a year on seats, about two-thirds with B/E Aerospace and Zodiac, said global consulting firm AlixPartners.
"It seems like a savvy move by Boeing," said a U.S.-based aerospace fund manager. Boeing "wouldn't be doing this if they didn't think it could grow."
Shares of Zodiac fell as much as 3.9 percent on Tuesday and closed at 17.10 euros ($19.46), down 2.5 percent, slightly underperforming the French market. Shares of B/E Aerospace fell 5.2 percent in early trading in New York. In late afternoon trading, the stock was down 0.6 percent at $45.85. Boeing stock was up 0.9 percent at $127.47.
"This could be very disruptive to the extent that Boeing decides to really push economy seats as seller-furnished equipment," said Ken Herbert, an analyst at Canaccord Genuity.
But he said many airlines will still buy from suppliers directly, especially "larger airlines that want commonality, and feel like they can negotiate better pricing on their own."
Boeing has 11 other suppliers whose seats are configured for its planes. But Boeing said on Monday the LIFT seats will be "optimized" to fit in the 737 interior with maximum width.
To the extent they increase direct purchases, Boeing and Airbus gain control over the risk that seats will fail to arrive on time. Like Boeing, Airbus still offers seats from other makers for airlines to choose.
Recaro Chief Executive Mark Hiller said the Airbus deal "created additional business for us" and there are many more orders it could pursue. "But we have to match the potential with what we can deliver," he said, noting Recaro aims to increase revenue by 10 percent a year.
LIFT by EnCore was started in 2011 by two industry veterans who sold a previous company to Zodiac in 2005. LIFT aims to deliver its first seats to Boeing in mid-2017 from a new, well-equipped factory in Huntington Beach, California.
Zodiac declined to comment. A spokesman for B/E Aerospace, Boeing's largest seat supplier, said LIFT was not a threat and that Boeing simply needed capacity that B/E could not provide at the moment.
"We have over 700 ship sets under firm contract for our Meridian seat, all for the 737 MAX, and we delivered the first to launch customer Southwest today," the spokesman told Reuters at the Aircraft Interiors Expo in Hamburg.
(Alwyn Scott and Victoria Bryan - Reuters)