Companies that follow Congress's suggestion and auto-enroll their employees in 401(k) defined-contribution retirement plans indeed see higher participation rates — 71 to 67 percent — but also appear more reluctant to chip in company matching funds, a study has found.

Though the matching rates are numerically close, 3.5 percent for non-auto-enroll companies and 3.2 percent for auto-enroll businesses — the study claims the disparity is statistically significant.

The Center for Retirement Research at Boston College, which released its findings this week, noted: "Firms with auto-enrollment may offset higher 401(k) participation costs by trimming their per-participant contributions."

Congress seven years ago passed enabling legislation to allow companies to auto-enroll their employees in their 401(k) tax-deferred retirement plans. The Boston College study is a follow-up to that legislation.