CFOs at small and midsize companies should monitor new 401(k) plan disclosure requirements. There are several new or forthcoming rules, and one in particular — ERISA Section 404 (a)(5) — could cause headaches. Plan fiduciaries have new obligations that carry substantial penalties and are likely to impose new costs.

Under that new rule, plan sponsors must (for plan years starting on or after November 1, 2011) prominently show on participants’ quarterly statements the administrative costs for running the plan, and on annual statements any investment-related fees.

Until now, such information has been buried in fine print, unlikely to be read. Now, the disclosures must be made in the same far-forward area of the statements that describes investment returns. Regulators hope this will improve awareness of plan costs and, where such costs are high, lead participants to push their employers to seek lower-cost plans. While most plans’ annual costs come to 1.5% of plan assets or less (in many cases, far less), for some plans the tab can be as high as 5%, says Lou Harvey, president and founder of Dalbar, an advisory firm that evaluates 401(k) providers.

Before, plans merely collected cost information from service providers. Now they will face the fiduciary obligation of determining that costs are “reasonable,” which generally means on par with what similar-size plans pay.

At the very least, companies may face incremental costs in fielding questions from employees once fees and expenses are made more conspicuous. More costly, if plan expenses are ultimately deemed unreasonable, appropriate changes must be made, which may even include changing providers. Even worse, if companies fail to take appropriate action, participants will have solid grounds to sue the plan, and the Internal Revenue Service may have grounds to disqualify it. “For the first time, plan sponsors face a real regulatory threat from the IRS,” Harvey says.

Companies, therefore, have plenty of incentive to prepare for these new requirements, but many finance chiefs are not yet up to speed, judging from an informal poll by CFO. A typical comment, from the finance chief at a $500 million energy company: “I’ve heard about it, but I don’t know any details.”

Some smaller companies may be even less aware, because many previously mandated 401(k) disclosures have not applied to small companies. And, notes Mark Ritter, executive director of compensation and benefits consulting for Grant Thornton, “as you go down in company size, the number of specialized benefits people dwindles, until you get to the point where maybe the CFO selects the investment options but no one is tracking new Labor Department regulations.”

Consider yourself warned.