Illinois just became the first U.S. state to adopt a new approach to a big problem in the nation's retirement saving system: the lack of workplace saving options for low-income workers.

Starting in 2017, companies that do not offer retirement plans will be required to automatically sign up their workers for a state-sponsored Roth IRA account, funded by a 3 percent (or higher) after-tax deduction from their paychecks, with the growth accruing tax-free.

The requirement applies to employers with 25 or more workers who have been in business at least two years, and workers can opt out if they choose.

Illinois will not be contributing to the new Illinois Secure Choice Savings Program (ISCSP) accounts, and investment management will be farmed to an outside firm.

The default investment will be a target-date fund, which reduces the allocation of higher-risk equities as the account holder gets closer to retirement, alongside four other simple fund choices.

The aim is to keep fees low -- not exceeding 75 basis points annually -- and far lower than that if the plan's sponsors have their way.

The new law puts Illinois at the vanguard of a growing movement to address the yawning gap in retirement savings for low-income workers. Initiatives are proliferating at the state and federal level, and the reasons are clear.

Ownership of retirement plan accounts has been falling sharply -- just 40 percent of households owned any type of account -- IRA, 401(k) or traditional pension -- in 2013, down from 48 percent in 2007, according to the Federal Reserve Board's triennial Survey of Consumer Finances released last September.

The Center for Retirement Research at Boston College estimates that at any given point, only half of U.S. private sector workers participate in a retirement plan.

In Illinois, 72 percent of private-sector workers in high-turnover, low-wage industries lacked access to a retirement plan, according to a study by the Woodstock Institute. By comparison, 70 percent or more of high-income workers are covered, industry data suggests. The study -- based on industry and federal government data -- found that ISCSP could potentially serve 2.5 million workers.

Plans like the ISCSP have been proposed in one form or another in more than half of the states.

"We've hit a critical mass on this concept," says Sarah Mysiewicz Gill, senior legislative representative at AARP, which has been working with proponents at the state level to advance the idea.

U.S. President Barack Obama has proposed creation of auto-IRAs at the federal level, and this year the administration is kicking off the myRA, a voluntary program aiming to help workers at companies that do not have retirement plans to set aside small amounts from their paychecks in a savings bond-like product.