Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE (I-Vt.) on Tuesday proposed raising Social Security taxes to extend the life of the entitlement program and increase benefits.

In a 12-page report, Sanders, the ranking member on the Senate Budget Committee and possible presidential candidate in 2016, argued Social Security's solvency problems could be solved if lawmakers simply lifted the cap on the tax that funds the program.

“If Republicans are serious about extending the solvency of Social Security beyond 2033, I hope they will join me in scrapping the cap that allows multi-millionaires to pay a much smaller percentage of their income into Social Security than the middle class,” Sanders said.

The Social Security trust fund that provides benefits to retired and disabled people is largely funded by the payroll tax. Right now, 6.2 percent of the payroll tax income from employees and employers is allotted to Social Security, and then that revenue is divided between the two funds.

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The amount of earnings that are subject to the payroll tax each year is capped, however, at $118,500.

Income above that level is not subject to the tax, which means an individual who makes more than $11 million a year, for example, would only pay into the fund on the first $118,500 of income.

“That is patently unfair,” Sanders said. “If we apply the Social Security payroll tax to income above $250,000, we could immediately bring in enough revenue to the Social Security trust fund to extend it for decades and also be able to increase benefits.”

The Social Security actuary, Sanders said, has projected that an increase of that size in the cap would extend the program past 2060.

The senator's proposal comes a day before the Senate Budget panel is scheduled to hold a hearing on the Social Security Disability Insurance Trust Fund, which is expected to be exhausted by the end of 2016.

Sanders slammed House Republicans for passing a rule in January that makes it more difficult to reallocate payroll tax revenue to keep the disability fund solvent.

Congress has approved six bills providing for 11 reallocations of the payroll tax between the retirement and disability funds. Lawmakers last approved such a measure in 1994.

If Congress allows the trust funds to borrow from each other, the Congressional Budget Office has projected both funds would remain solvent until 2030.

Republicans say Social Security is facing a funding crisis that must be addressed head-on by the Congress.

--This report was updated at 3:16 p.m.