As the New York Times reports, several states have created state-based retirement savings plans. The U.S. Department of Labor (DOL) has now issued guidance for states on the issue. According to the DOL press release, this is necessary because

A lack of clarity of this area of the law has made other states reluctant to move forward with plans to create additional retirement savings opportunities for workers.

A Governmental Accountability Office (GAO) report from September that looked at how to expand private sector retirement coverage explains how these state plans could conflict with the Employee Retirement Income Security Act (ERISA):

Generally, ERISA preempts, or invalidates, any state law relating to "employee benefit plans" for private sector workers, but different areas of uncertainty arise based on the details of each state effort.

So, the DOL has published a notice of proposed rulemaking that

would provide a new safe harbor from ERISA for state-sponsored IRAs that conform to certain provisions. The proposal would adopt a standard stating that state-sponsored payroll deduction IRA programs must be "voluntary" for workers, rather than "completely voluntary" as defined in a 1975 rule. This will allow for automatic enrollment of employees in such programs so long as they are given the ability to opt-out, and employers are minimally involved. For instance, employers would make the automatic deductions from employee paychecks, but the employees and states would retain control of the program and IRA accounts. Employers could not prevent workers from declining to participate in the program.

Additionally, DOL has published an interpretive bulletin

regarding the creation of state-based ERISA-compliant 401(k) plans that are open to businesses and workers. In addition to payroll deduction IRAs and state-based 401(k)s, the bulletin gives several examples of approaches to creating state retirement savings programs that may avoid being preempted under ERISA.

The NYT notes,

Washington State is pursuing another approach: It enacted a law that will create a retirement plan marketplace for small businesses, where participation is entirely voluntary. Financial services firms would compete to join the marketplace by meeting a certain cap on fees and other requirements around transparency, [senior legislative representative for AARP Sarah] Mysiewicz Gill said.

This law is SB 5826, enacted this year. The state Department of Commerce expects the marketplace to be operational in 2017.

The GAO report looks specifically at the plans created in Washington, California, Illinois, Massachusetts, Maryland and West Virginia. There's a table comparing the key parts of each plan on pages 27-28.