Fidelity FundsNetwork has urged regulators and the Treasury to urgently clarify its rules on adviser charging.
Head of tax Paul Kennedy said advisers needed to be aware that facilitating a fee would count towards a client's capital gains tax allowance, currently at £10,600.
"Previously where the platform, fund manager and IFA were all paid out of the product, the payment of your remuneration was being paid before any investment return was being taxed, and it also meant your remuneration was completely blind to the client's tax," he said.
"Facilitating fees has turned it on its head. All a facilitated fee is, is a client telling us to cash in investments to meet your fees, and they could be cashing in their investments for any other reason.
"We need to be conscious of the effect it may have on the client's tax position."
The responsibility for the taxation implication of adviser charging falls between the Financial Services Authority (FSA), HM Revenue & Customs (HMRC) and the Treasury.
Clarification had been slow to arrive, Kennedy said.
"The FSA in 2010 said they weren't changing tax law, [but] the move to fees was going to change the taxation position of the client," he said.
"They in conjunction with Treasury and HMRC said they would make sure it was sorted out before RDR. It started being looked at just a few weeks ago, but will get clarity we hit before hit RDR."
Last year, the Investment Management Association warned adviser charging would have a "perverse" impact on client CGT.
Beware ‘sting in the tail’
Still 66% women in lower quartile
Led by Aberdeen Standard Investments
Introducing admin fee
Effective from June 2019