U.S. Rep. Cheri Bustos was among a group of more than 110 lawmakers who are urging President Barack Obama not to include a proposal to trim Social Security benefits in his 2015 budget proposal.
The president's budget is due out in two weeks.
The letter, which was signed by 117 members of the U.S. House, all Democrats, asked him not to "place the burden of additional deficit reduction on the backs of seniors, veterans, federal retirees and others ..."
Obama has said that he is open to a debt reduction deal that includes changing the way cost-of-living adjustments are figured for some federal programs.
Known as "chained CPI," the change would slow the rate of growth in programs such as Social Security by tying it to a different way of measuring the change in the consumer price index.
Supporters of the change say it better reflects the change in prices, but critics say it doesn't adequately account for how rising prices, particularly in health care, affect older Americans.
Reps. Allyson Schwartz, D-Pa., is leading the effort along with Jan Schakowsky, D-Ill., David Cicilline, D-Rhode Island, and Bustos and Rep. Bruce Braley, D-Iowa. Rep. Dave Loebsack, D-Iowa, also signed onto the letter.