Reducing contribution limits or replacing tax deferrals with a tax credit "could dissuade small employers from sponsoring plans," Falcon says. "If the tax benefit to small-business owners is limited, they could choose to avoid the costs of setting up a retirement plan."

White, of David B. White Financial, agrees. "Employers are going to drop plans. A big factor in small businesses is that if it doesn't benefit the top people, they are going to cancel it, and that is going to hurt the small people too."

He sees the changes as "just another diabolical redistribution-of-wealth scheme. It is another way of hiding a tax hike. All you are doing is robbing Peter to pay Paul and moving money from one pocket to another. The biggest thing is that you are going to hurt the economy, and you are going to hurt savings."

White sees the current system of pretax contributions as an important savings tool.

"The reason 401k's are more successful that IRAs is because of the automatic withholding that is done for them, because it comes out first instead of last," he says.

In December, the National Commission on Fiscal Responsibility and Reform released its document on federal debt reduction, titled "The Moment of Truth."

"Although their guiding principles and values specifically mention the need to keep America sound over the long run by implementing 'policies today to ensure that future generations have retirement security, affordable health care and financial freedom,' the document puts forth a tax reform plan that would modify retirement plans by capping annual tax-preferred contributions to (the) lower of $20,000 or 20% of income," says Jack VanDerhei, research director for the Employee Benefit Research Institute.

"This is often referred to as the 20/20 cap. This alternative formulation of capping tax-preferred contributions would substantially reduce the current limits available under qualified defined-contribution plans," such as 401ks, VanDerhei says.

The current combination of employee and employer contributions is the lesser of a dollar limit of at least $49,000 per year and a percentage limit of 100% of an employee's compensation.

"The 20/20 cap would, as expected, most affect the highest-income workers, but it also would cause a significant reduction in retirement accumulations for the lowest-income workers," VanDerhei says.

A similar take on the matter is expressed by the Pension Rights Center.

"The reason Congress conferred preferential tax treatment is because policymakers recognize how hard it is for people to save for retirement -- particularly low- and moderate-income workers," said Karen Friedman, the executive vice president and policy director of the center, in her Senate testimony.

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"These incentives are meant to encourage employers to set up plans and to encourage employees to save," she continued. "However, the incentives end up disproportionately benefiting the nation's most affluent employees, who would almost certainly save for retirement even without tax incentives. Two-thirds of the value of tax expenditures for retirement savings plans goes to households in the top-income quintile."

Friedman's organization would support tax reform to "limit leakage," meaning withdrawing money from plans before retirement.

"The main tax provision to control leakage is a 10% excise tax on certain pre-retirement use of retirement savings, which has served primarily as a steep and unfair additional tax on the poor and the middle class, while doing little to actually control the problem," Friedman said. "Congress could create voluntarily designated 401k's and IRAs that once designated could not be accessed prior to retirement -- and use carefully targeted tax incentives directed at both employees and employers to encourage the use of such lock-down accounts. Moreover, the Saver's Credit itself might be locked down so that the credit amount is not available until retirement."