Cutting Social Security benefits is likely to create problems for those who receive the benefits, the letter said.
"We believe that cutting Social Security benefits, beyond the already scheduled increase in the retirement age from 65 to 67, will create even greater hardship for our most vulnerable citizens."
A panel of Social Security experts on Friday were divided on how President Obama will handle entitlement reform in next week’s address.
Those looking at ways to reduce the deficit say they hope Obama will use the speech to begin a bipartisan drive toward a balanced budget by seizing the initiative from House Republicans on spending.
They have argued Obama should go beyond the non-security discretionary spending cuts the GOP is seeking by embracing cuts to defense spending as well as tax code and entitlement reform.
"There are many people on both sides of the aisle, especially in the Senate who want to see him do that,"said Maya MacGuineas, the president of the Committee for a Responsible Federal Budget who spoke at a Capitol Hill event organized by The Urban Institute.
Rudolph Penner, a fellow at the Urban Institute, predicted that the president won't announce his support of overhauling entitlements and, instead, will focus on cutting discretionary spending.
Erik Wasson contributed to this report.