The FSA has been urged to examine the disclosure of commissions by property managing agents following claims that some are inflating tenants' premiums.
The managing agents are understood to have found a "legal loophole" allowing them to pump up premiums before selling insurance onto tenants.
The higher rates earn them enhanced commission rates from insurers.
A senior market source said he had known property managers to top up premiums by "considerably more than 50% so they can make major profits."
Lucy Cummings, commercial director of property managers Erinaceous, said the procedure stemmed from the post 9/11 era when managing agents wanted to "protect income" from rising rates.
She said Erinaceous always disclosed commissions when asked, but that she had "some concerns" about other firms' lack of disclosure. She added that Erinaceous would monitor how the FSA will "address the control of commissions".
But an FSA spokesman said the FSA will not look into the issue as property managers sit outside its regulatory remit.