Among the middle-income seniors likely to be affected are federal retirees covered by the Civil Service Retirement System - the government's legacy defined benefit pension system.
These retirees did not participate in Social Security during their time in the federal workforce (federal workers hired since 1987 have participated in the newer defined benefit Federal Employees Retirement System, and they receive Social Security.)
This also applies to state government employees, most of whom participate in defined-benefit pension plans and are not covered by Social Security during their tenure as state employees.
Another big area of worry: low-income "dual-eligible" seniors who receive Social Security and also participate in both Medicare and state-run Medicaid programs.
Although this group is not covered by the "hold harmless" provision, states pick up the tab for the higher cost, putting additional pressure on already-stressed state Medicaid budgets.
"We're very concerned about state Medicaid budgets, and how they would handle the increase," says Andrew Scholnick, senior legislative representative at AARP.
Although Congress has a busy fall schedule, lawmakers are showing interest in taking action to mitigate the impact. "I think it's is going to come to the forefront a bit more now," says Scholnick.
But he doubts Congress will act before October, leaving the door open to a last minute fix before year-end.