The heartening news from this year's study is that for all employers, including the 390 with more than 500 employees, the majority are invested in their workers' retirement futures: 74 percent of respondents offer some form of a defined contribution plan.

Related: Competition in smaller retirement plan market heats up

Among large employers, 92 percent are offering a savings plan, but the number drops to 72 percent for employers with fewer than 100 workers.

This year's findings come as the groundswell of lawmakers, policy advocates, and now industry stakeholders calling for mandatory automatic enrollment continues to grow.

More than half of the states in the union are at least exploring legislation that would expand access to workplace retirement plans via state-sponsored plans. Several states, including Connecticut, Illinois and California, will mandate auto-enrollment for small employers.

Dissonance about retirement plans

Now industry is getting more vocal in advancing mandated participation in retirement plans. Last week, Ronald O'Hanley, CEO of Boston-based State Street Global Advisors, wrote an open letter to Congress, calling for federal, bipartisan legislation that would require all private-sector employers to auto-enroll all employees — including part-time workers — in a defined contribution plan.

"Time is not on our side, and the cost of inaction is great," wrote O'Hanley in his letter to Congress, arguing that comprehensive retirement policy at the federal level is needed to replace the "patchwork" of initiatives at the state level. Though well intended, O'Hanley said that patchwork will "lead to a complex and inefficient set of retirement savings programs that perversely could lead to lower savings levels."

Beyond claiming they were not big enough to sponsor a plan, Transamerica also found that the expense of offering a plan is discouraging employers: 50 percent of employers without a plan cited cost as the primary reason.

Nearly one-third of nonsponsoring employers claimed their employees were not interested in a retirement plan.

That reasoning suggests some dissonance in nonsponsoring employers' perspective. As a part of its annual survey, Transamerica also surveyed plan participants, 89 percent of whom view their retirement plan as an important benefit.

Perceived administrative complexity and fiduciary risk were relatively low deterrents: 19 and 13 percent of nonsponsoring employers cited those as the top reasons, respectively.

Transamerica also found significant discrepancy between large and small plans' adoption of automatic enrollment features.

About four in 10 large plans automatically enroll employees, compared to only 18 percent of plans with fewer than 100 participants. For all plans, only 21 percent of sponsors have adopted an auto-enrollment feature.

Sponsors' level of adoption of automatic enrollment lags participants' openness to the feature, according to Transamerica's study. Across plans of all size, 71 percent of participants found both auto-enrollment and auto-escalation features appealing.

Catherine Collinson, president of the Transamerica Center for Retirement Studies, noted that employer adoption of auto-enrollment is low, despite the feature being one of the most effective tools to increase participation rates, and its appeal to workers.

The median default contribution rate for automatically enrolled workers in all plans is 3 percent, according to the Transamerica Center.

The study echoed a commonly aired concern among retirement experts relative to the unintended consequence of automatically enrolling employees at a 3 percent deferral rate, which "may be misleading to participants by implying that it is adequate to fund an individual or family's retirement when in most cases, it is not."