The plane maker continues to deal with a safety crisis after a panel blew off a flight in midair in January, leading to probes into the incident and the company's production process.
Southwest said it expects deliveries of Boeing's MAX jets to fall 42% this year from previous estimates which will likely cut its 2024 capacity.
It is the second time the carrier reduced its delivery forecast since January and CEO Bob Jordan said he would not be surprised if it changed again.
Southwest's stock plunged as much as 15%.
United Airlines CEO Scott Kirby said Tuesday deliveries are also going to be way behind this year.
Last week, the company said it was pausing pilot hiring for two months.
United's stock fell as much as five percent.
But shares of Alaska Air Group fared better Tuesday, rising as much as four percent.
The airline which operated the 737 MAX jet which lost part of its fuselage in midflight said its 2024 capacity plans were still in flux due to the Boeing crisis.
The plane manufacturer's shares dropped as much as five percent after the New York Times reported that the recent FAA audit of its 737 MAX production found numerous problems.
