Insurers and money managers will benefit to a far greater extent than advisers from the Government's pledged guidance for retirees, SimplyBiz Group said.
The firm called on the FCA to reflect this and to make the levy fairer than its original proposals, which suggested advisers being liable for either 30% or 20% of the costs.
In its Consultative Paper CP14/11, the FCA asked respondents if there was a fairer third option.
Ken Davy, chairman of the SimplyBiz Group, said: "The benefit to advisers from the guidance guarantee is likely to be approximately £12.5m per year.
"It is essential to note however that this is not a cumulative benefit.
"For the other fee-blocks, the benefit is c£39m a year on a cumulative basis.

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"Therefore, within just 5 years, the insurers and money managers will have received a total of approximately £549m, compared to the advisers total of c£62m, and be receiving an annual income 14 times greater than that of advisers."
Mr Davy said: "The gap highlighted and its inequality will continue to worsen year by year on a cumulative basis to the increasing disadvantage of advisers.
"We have seen with the Investors Compensation Scheme Levy, which continues to place a wholly unfair burden on advisers, how the unintended consequences of regulatory action can damage the sector.
"We are also very concerned that the guidance levy is handing a blank cheque to the organisations tasked to deliver the guidance.
"We are not against the guidance service itself; however it is vital that the costs are shared equitably and properly controlled.
"Our detailed response to the FCA demonstrates that the adviser fee-block proportion should more properly be of the order of 6% or less, rather than the 20% or 30% suggested".