Southwest Airlines on Wednesday confirmed plans to significantly reduce the number of flight attendants and pilots based in Atlanta and cut flights at Hartsfield-Jackson International Airport early next year by a third.

The cuts are a substantial change for an airline that entered Atlanta more than a decade ago through its merger with AirTran Airways and promised to be a low-cost rival at the world’s busiest airport to top dog, Delta Air Lines. Southwest is the No. 2 carrier at Hartsfield-Jackson.

Dallas-based Southwest is under increasing shareholder pressure to improve performance and is scheduled to hold a meeting with investors on Thursday. Southwest also has been strained by manufacturing challenges at Boeing, the supplier of all its airliners.

The low-cost carrier plans to eliminate more than 300 pilot and flight attendant positions out of Hartsfield-Jackson early next year, but not eliminate its Atlanta crew base. The cuts were first reported by CNBC.

The changes will affect some 200 flight attendants and up to 140 pilots. The moves are not layoffs, but instead affected workers would bid to work routes through other cities.

By March of next year, Southwest said it will have 381 Atlanta departures throughout the week, a third less than 567 currently.

“Although we try everything we can before making difficult decisions like this one, we simply cannot afford continued losses and must make this change to help restore our profitability,” Southwest said in a memo to employees obtained by The Atlanta Journal-Constitution. “This decision in no way reflects our employees’ performance, and we’re proud of the hospitality and the efforts they have made and will continue to make with our customers in (Atlanta).”

Transport Workers Union of America Local 556, the union that represents Southwest flight attendants, expressed outrage.

Alison Head, a Southwest flight attendant who represents the Atlanta base on the Transport Workers Union’s executive board, said while the more than 800 flight attendants based out of Hartsfield-Jackson will be able to keep their jobs, their positions will be in other cities, meaning major disruptions for those workers.

“The flight attendants are disappointed in management and poor management decisions, and ultimately, they are paying the price for those poor decisions,” Head said in an interview. The reductions will have a “ripple effect across all our bases.”

The move will “uproot families,” and there likely will be some long-tenured workers who opt to leave, she said.

The reductions in service mean Southwest will need fewer crew members in Atlanta, though the airline said it will boost service in other cities, including Nashville, Tennessee.

“We continue to optimize our network to meet customer demand, best utilize our fleet, and maximize revenue opportunities,” Southwest spokesman Chris Perry said in an email. “Decisions like these are difficult for our company because of the effects on our people, but we have a history of more than 53 years of ensuring they are taken care of.”

In April, the AJC reported Southwest planned to reduce flights to and from Atlanta and pull out of some other airports, as its operations come under pressure from delays in deliveries of Boeing aircraft.

Southwest has an all-Boeing fleet of 737 aircraft, and delays and other issues with the MAX line of airliners have stressed Southwest’s fleet planning.

The carrier has also been under pressure from shareholders to improve performance with activist investor Elliott Investment Management pushing for the ouster of Southwest CEO Bob Jordan.

In April, Southwest operated up to 119 departures a day from Atlanta and the company said that figure would decline to 94 daily departures maximum from Atlanta on weekdays in the airline’s revised summer schedule, airline spokesman Dan Landson said at the time.

Head said Southwest currently operates about 80 flights a day and that figure will fall to fewer than 60 per day with these new changes.

It’s unclear what impact the service reductions will have on ground crew members.

Bill Bernal, president of Transport Workers Union of America Local 556, said in a statement, “management continues to make decisions that lack full transparency, sufficient communication with union leadership, and most alarmingly, a lack of focus on what has made the airline great, the employees.”

According to Perry, the airline is permanently cutting routes between Hartsfield-Jackson and Cleveland; Greenville, South Carolina; Jackson, Mississippi; Memphis, Tennessee; Miami; Fort Myers and Sarasota, Florida; Milwaukee; Oklahoma City; Omaha, Nebraska; Philadelphia; Richmond, Virginia; and Louisville, Kentucky. Only two trips will be provided for Fort Lauderdale and Jacksonville, Florida, per week.

In a statement, Hartsfield-Jackson said it “is fully prepared to address any challenges stemming from changes with Southwest Airlines. As a top destination for airlines, ATL remains in high demand. We will continue delivering top-tier service and efficiency for all our passengers and stakeholders.”