In a new ad, Pryor argues Rep. Tom Cotton (R-Ark.) voted to cut Social Security and turn Medicare into a voucher program when he supported a conservative budget rejected by the House earlier this year.
The ad then says Pryor supports cutting billions in waste from entitlement programs, and to provide for lower prescription drug costs and more preventative care.
"I support this message because cutting waste and fraud is responsible, but cutting benefits isn’t,” Pryor says at the end of the ad.
The 30-second ad is running statewide, Pryor’s campaign said.
Pryor is targeting Cotton for backing the Republican Study Committee's budget.
It would raise the eligibility age for Social Security from 65 to 70, and would shift Medicare into a premium support program, which Democrats say would resemble a voucher program. It would also have adopted a less generous formula for raising Social Security benefits for inflation.
The budget was rejected by the House, but won support from the most conservative Republicans.
Pryor is seen as one of the most vulnerable Democrats running for reelection to the Senate in 2014.
He voted in favor of the new healthcare law, and Cotton is expected to make that an issue in their campaign. Cotton must first win the Republican nomination for the Senate race.
This story was updated at 12:34 p.m.