St. Vincent employs more than 3,000 physicians and 18,000 other employees. St. Mary has 750 physicians and more than 3,500 other employees.
St. Vincent spokesman Johnny Smith said the number of jobs being cut is undetermined.
"At this time, there's not a designated number," Smith said. "We're looking at all administrative costs, labor, supply, programs and services."
Asked if St. Vincent was considering closing any of its hospitals, Smith replied: "We're still in the evaluation and discernment process."
The St. Vincent network includes one recently opened hospital in the booming Indianapolis suburb of Fishers and older community hospitals in Anderson, Bedford, Brazil, Elwood, Frankfort, Kokomo, North Vernon, Salem, Williamsport and Winchester.
The two hospital groups issued nearly identical news releases saying they were facing challenged budget shortfalls, decreasing reimbursement, and the national health care overhaul's mandated reduction in payments.
St. Vincent CEO Vincent Caponi and Tim Flesch, president of St. Mary's Health, each issued statements saying, "To sustain our health system's service to patients and families ... we must re-imagine the way we provide holistic care - body, mind, and spirit."
Allegiant's website says it is the nation's largest Catholic and nonprofit health system and the third-largest system based on revenues in the U.S.