From left, Sen. Tom Harkin, D-Iowa, Sen. Sherrod Brown, D-Ohio, and Sen. Jack Reed, D-R.I., are backed up by students during a news conference on Capitol Hill in Washington, Tuesday, May 8, 2012, as the Senate moved toward a showdown on a Democratic proposal to keep federally subsidized loan interest rates from doubling for millions of college students. (AP Photo/J. Scott Applewhite) Sens. Tom Harkin (D-Iowa), left, and Sherrod Brown (D-Ohio) (J. Scott Applewhite/AP)

As some Republicans in Congress push to scale back and otherwise reform entitlement programs, a pair of liberal senators are pushing to expand one of the programs — Social Security.

Sens. Sherrod Brown (D-Ohio) and Tom Harkin (D-Iowa) are spearheading the effort, which they say would increase benefits for all Social Security beneficiaries by about $70 per month, change the cost-of-living calculation for benefits, and increase the amount that the wealthiest Americans pay into the program.

Social Security taxes are currently capped at the first $113,700 of someone's income. Brown and Harkin say the tax increase would help sustain the program, which is solvent but is on track for significant deficits in future decades.

"Seniors have spent a lifetime paying into Social Security, but as the cost of living continues to rise, the budgets of many are stretched to the breaking point," Brown said in a statement. "That is why Congress needs to do more to ensure that our seniors receive the benefits they’ve earned so that they can continue to retire with dignity. The Strengthening Social Security Act of 2013 would do this by expanding benefits, strengthening the program’s future and making retirement more secure for all Americans."

Brown and Harkin have also launched a petition, in tandem with the Progressive Change Campaign Committee.

Entitlement reforms are a significant subplot of the looming budget negotiations on Capitol Hill. Republicans have aimed for changes to how Medicare is administered, including proposing a voucher system, and have suggested upping the retirement age for Social Security or privatizing it, among other changes.