NEW YORK (Bloomberg) - Aon Corp., the insurance broker that said on Friday it may resume taking payments previously banned by former New York Attorney General Eliot Spitzer, drew criticism from a group representing some of its clients.

"We're very disappointed in the decision" by Chicago-based Aon to accept so-called contingent commissions, Amy Benson, a spokeswoman for the Risk and Insurance Management Society, or RIMS, said in a telephone interview. "It hurts consumers. It imposes an inherent conflict of interest."

Aon is considering bringing back the once-secret payments from insurers to supplement the fees it takes from the buyers of coverage. Insurance brokers help clients find the best deal for policies protecting factories from storm damage and corporate boards from shareholder lawsuits. Aon, the world's biggest broker, has posted profit declines in four of the last seven quarters as the sluggish economy curbed insurance demand.

Contingent commissions, which insurers pay to entice Contingent commissions, which insurers pay to entice brokers, vary in amount based on the quantity of coverage sold by the middleman and how profitable the policies turn out to be for carriers. Spitzer, who conducted the probes and imposed the restrictions, said the fees could put the interest of the broker and client in conflict.

"By taking contingent commissions you have yet another potential source of revenue," said Paul Newsome, an analyst with Sandler O'Neill & Partners LP in Chicago. "And that is going to be an offset to the ongoing pressure on revenue."

CEO Greg Case, who took over in 2005 after Aon reached a $190 million settlement with Spitzer, is expanding the broker's consulting business as the US insurance market contracts. On July 12, Aon agreed to buy Hewitt Associates Inc. for $4.9 billion to expand its employee pay and benefits advisory practice.

Aon, Marsh & McLennan Cos. and Willis Group Holdings plc., the three biggest brokers, were released in February from restrictions on accepting contingent commissions, the payments that had prompted Spitzer's bid-rigging probes. Under the new rules, brokers must reveal the compensation if asked by clients.

The companies had resolved Spitzer's allegations of fraud and anti-competitive practices, with Marsh & McLennan agreeing to pay $850 million and No.3 Willis $50 million.

"Aon has focused on value for price for the last five years, which coincides with our not taking contingents," David Prosperi, a spokesman for Aon, said in an e-mail. "We must provide the best value for what we get paid. It must be clear to our clients that the value we provide to them is substantially greater than the price they are paying for that value."

"RIMS has always maintained the position that contingent commissions should be universally banned and views Aon's intentions as a step backwards with regard to the level of service it provides to its clients," the insurance buyers' group said in a statement.

Aon and New York-based Marsh & McLennan appealed to officials for redress in 2008 as regulators opened a review. Marsh & McLennan, which was the No.1 broker at the time of Spitzer's probes, said in 2004 that the payments totalled about $845 million a year, or 12 percent of brokerage revenue. London- based Willis has said it won't take contingents and on Friday called Aon's stance "troublesome and ambiguous".

"Aon's overdue and muted announcement, floated in mid-summer, should come as a wake-up call to all risk managers and buyers of insurance to re-evaluate whether their broker really works for them, or the insurance carrier," Willis said in a statement.

Marsh & McLennan said on March 24 it will take contingent commissions on business done by its unit serving mid-sized US clients. The firm won't take contingent commissions on business for US clients in its "core broking operations", according to a statement.

"The contingent commissions created inherent conflicts and tensions that led to improper practices that we were trying to eliminate," Spitzer said in an interview in February after the New York Insurance Department repealed the ban.

Spitzer left his post without extending the fee ban to smaller agents. He went on to become governor of New York, a position he resigned in 2008 amid a prostitution scandal. In the last two years, Aon, Marsh & McLennan and Willis called for common rules to be applied to all middlemen.

Willis, led by CEO Joseph Plumeri, accepts contingent commissions stemming from business it gained through the $1.7 billion acquisition of Hilb Rogal and Hobbs Co. in 2008. Under previous rules, the big brokers were given a grace period after completing a takeover to take contingent commissions on business generated by the acquired company. Those payments fell 60 percent to $8 million in the first quarter, Willis said.

"We have decided to accept various forms of compensation available, which may include supplemental and/or contingent commissions," said Steve McGill, CEO of Aon Risk Solutions, a division of the Chicago-based company, in a statement on Friday.