Employers should start by making sure they're at least a chapter or two ahead of employees in this process, says Gregory Ash, partner at law firm Spencer Fane Britt & Browne and chairman of its ERISA litigation group.

"The very first thing that every employer should do is to thoroughly understand the fees that are being assessed at every level with respect to the plan," Ash says. "If employers don't understand the fees to begin with, they can't answer questions."

Next, type up a document that provides answers to the anticipated questions, suggests Robert Liberto, senior vice president at Segal Advisors. A Q&A that explains why certain decisions were made, and how the employer selected the investment choices "will help defray a lot of questions," Liberto adds.

Ash also suggests working out the process for handling questions that do come in, including the person in charge, the turnaround time and whether questions will be documented.

It's a teachable moment for participants. There's an opportunity to explain why certain fees are charged and why a more expensive actively managed fund might be worth it, if the performance is there, experts agree.

However, companies should definitely take this opportunity to make sure their 401(k) plan's expenses are moderate, urges John Kent Graham, vice president and regional director of compliance research at Sibson Consulting. "The question is, 'Is this a reasonable cost of administration?'" he says, adding that plan sponsors "basically have a little bit more than a year to get their plans where they want them to be."