The FCA announced the much awaited changes for Sipp operators on Monday.
AMPS has particularly questioned the use of assets under administration as the basis for calculating capital adequacy.
It fears the move could have major implications, possibly even causing some Sipp firms to fail.
In a statement, it said: "AMPS has serious issues with the use of AUA as the basis for calculating capital adequacy for a number of reasons.
"If the value of assets falls but the number of Sipps remains unchanged, then the capital adequacy requirements reduces but the costs remain the same.
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"In terms of the non-standard assets these are hard to transfer and may have a low or even negligible value at that time, leaving insufficient capital to meet on going costs.
"Finally a demand for a cash injection at short notice such as a 10% increase in value of AUA can result in a 5% increase in capital adequacy. Such an increase for additional capital could force perfectly good Sipp firms to fail."
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For more on the new rules and reaction click HERE.