Association President Dr. Bruce Malone says that would mean more elderly people would lose their doctor and have a harder time finding a new one.
The group wants federal lawmakers to fix the payment formula so it doesn't end up penalizing doctors financially.
The Fort Worth Star-Telegram reports that physicians will see a 29.6 percent cut in reimbursements starting Jan. 1 if Congress doesn't act.
Malone says physicians love their Medicare patients but they can't afford to continue to care for them if Medicare doesn't cover the cost of doing so.
Most people become eligible for Medicare when they turn 65.