Last month, Sen. Jeff MerkleyJeffrey (Jeff) Alan MerkleyBill to bolster gun background checks gains enough support to break filibuster Democrats remain skeptical of Trump’s rebuilding plan Dems to face off in Calif. nomination fights MORE (D-Ore.) announced plans to introduce a bill to increase the annual cost-of-living adjustments for Social Security.  He proposed to pay for it by raising the Social Security payroll tax rate of the wealthiest Americans -- those who make more than $250,000 per year -- closer to the rate already paid by middle and working class American workers.

Many people don’t know that any income above $117,000 per year is not taxed by Social Security (this limit on the amount of earnings subject to the tax is adjusted annually to keep up with inflation). That means that someone who makes twice the cap this year – $234,000 – pays the tax on only half of his or her wages. And those lucky enough to make at least $1.2 million per year are taxed by Social Security on less than one-tenth of their income.

In other words, workers who make $117,000 or less per year – the vast majority, as a recent analysis by the Center for Economic and Policy Research shows -- pay a higher Social Security payroll tax rate than the 5.6 percent who make more.

Merkley will be joining Sen. Bernie SandersBernard (Bernie) SandersAnti-abortion Dem wins primary fight Lipinski holds slim lead in tough Illinois primary fight Overnight Defense: Senate sides with Trump on military role in Yemen | Dem vets push for new war authorization on Iraq anniversary | General says time isn't 'right' for space corps MORE (I-Vt.) and Rep. Peter DeFazio (D-Ore.), who also have introduced bills to apply the Social Security payroll tax to wages above $250,000. These bills are similar to a proposal by Barack ObamaBarack Hussein ObamaWater has experienced a decade of bipartisan success Kentucky candidate takes heat for tweeting he'd like to use congressman for target practice What’s genius for Obama is scandal when it comes to Trump MORE during the 2008 presidential campaign. The Social Security Administration’s Chief Actuary estimates that the payroll tax cap sections of these proposals would reduce the program’s long-term budget shortfall by about 80 percent.

Others have proposed increasing or phasing out the Social Security payroll tax cap entirely, a concept popularly coined as “Scrap the Cap.” Sens. Tom HarkinThomas (Tom) Richard HarkinSenate GOP rejects Trump’s call to go big on gun legislation Trump should require federal contractors to follow the law Orrin Hatch, ‘a tough old bird,’ got a lot done in the Senate MORE (D-Iowa) and Mark BegichMark Peter BegichPerez creates advisory team for DNC transition The future of the Arctic 2016’s battle for the Senate: A shifting map MORE (D-Alaska), as well as Reps. Linda Sanchez (D-Calif.), Ted Deutch (D-Fla.) and Gwen MooreGwen Sophia MoorePelosi rips Trump administration's 'thought control' on CDC Dem: Trump banning words in CDC documents ‘deeply disturbing and offensive’ Dem rep: Moore supporter called my office pretending to be a reporter, shouted racial slurs MORE (D-Wis.), have introduced bills that would phase out the cap over five to ten years. The phase-outs of the cap in these proposals are estimated to eliminate 70 to 80 percent of the long-range shortfall.

While every one of these senators and representatives earn over $117,000 annually, Census Bureau data shows that only about 1 in 18 workers would pay more if the cap were scrapped, and only the top 1.4 percent (1 in 71 workers) would be affected if the tax were applied to earnings over $250,000.

It gets even more interesting when you look at different states and slices of the population.  In the home states of Merkley, Harkin and Sanders (Oregon, Iowa, and Vermont), the top 4.2 percent, 3.5 percent and 4.0 percent of workers, respectively, would pay more if the Social Security payroll cap were phased out.

Even fewer women workers would be affected if the cap were abolished: only about 1 in 36 (2.8 percent) of them would pay more, and the top half of one percent would be affected if the tax were applied to earnings over $250,000.  Similarly, only about 1 in 50 black or Latino workers would pay more if the cap were lifted entirely, and about 1 in 200 would be affected if earnings above $250,000 were subject to the tax.

As the retirement security of working Americans continues to be an important topic of debate, these proposals -- to strengthen Social Security by having the wealthiest Americans pay the same payroll tax rate as the rest of us – deserve the utmost consideration.

Woo is the director of Domestic Policy at the Center for Economic and Policy Research, a progressive economic think-tank.