When assets in the retirement plan at Axis Global Logistics of Minnesota, a 30-employee Minneapolis-area shipping company, hit $1 million, Vern Langer, who oversees the plan, expected fees to drop. But when he carefully tallied up the costs, he got a nasty surprise. The plan provider "was getting almost twice what it said it was," says Langer, who dumped the provider in February in favor of a cheaper one.

It's a fair bet that in the coming months, many more workers will have a similar rude awakening: New federal 401(k) disclosure rules go into effect this summer. The new Labor Department regulations will force 401(k) providers at all companies to state more clearly the gamut of fees they charge for running workplace retirement plans. But, industry insiders say, the most eye-popping cost disclosures are more likely to be found at smaller plans (those with fewer than 500 members), a segment that accounts for a quarter of all 401(k) holders today. Indeed, one recent study found that workers in plans with less than $1 million in assets paid average fees totaling $141 per $10,000 invested -- more than three times the rate in larger plans.

That huge difference, pros say, doesn't come from malfeasance, typically, but rather from scale: Fortune 500 companies can pool thousands of workers' savings, splitting overhead and still sparing money for specialists to vet the plan. Mom-and-pop shops generally have neither the negotiating power to demand discounts from providers nor the expertise to spot bloated costs and other problems -- especially when the in-house administrator is left to juggle scores of other tasks as well. "There's a lot of things to do to keep a company running," says Sharon Hughes, who oversees the 401(k) at Diamond McCarthy, a 70-person Texas law firm, in between duties that range from hunting for office space to doing the annual audit. For the 401(k), she gets a little help from a financial adviser and three firm lawyers. "I try to pick somebody that has numbers in their background," she says.

Still, small plans have their advantages. Workers are more likely to get personalized advice, say pros, because a single financial adviser can serve the entire office. And, of course, if the new 401(k) disclosures reveal that you're paying too much in fees, it may be easier to go straight to the boss with your complaint.