The body, whose member firms manage £600 billion of wealth in the UK and Ireland, has expressed concerns about the impact that the new Markets in Financial Instruments Directive deal will have on the UK.
WMA deputy chief executive John Barrass said: "MiFID and the RDR have different definitions of independent and restricted services, which could mean that the UK has to change its rules again barely a year after a significant overhaul.
"The agreed MiFID appears to permit an override by national regulators to enable them to continue to impose their own rules, but whether that means the RDR survives is unclear.
"Does this mean that RDR will continue, unaffected by this EU-wide agreement?
"And if it does will it put UK firms at a disadvantage to continental ones covered by a different and less onerous régime?"
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The WMA, which represents 182 firms, welcomed the so-called trilogue agreement between the European Parliament, Commission and Council for enabling firms to develop their plans to accommodate future reforms.
The WMA said its work contributed to constructive changes to otherwise onerous requirements which would have impacted on suitability tests for investors, execution only stockbroking services and the ability to trade in investments from non-EU countries.