The IPA's director-general, Hamish Pringle, said he was shocked by the U-turn. The legislation, which only came into force in April, required disclosure by quoted companies of relevant non-financial information, including marketing measures.
'We feel as if we have been led up the garden path only to find the gate slammed shut,' added Pringle.
Brown announced his decision at the CBI's annual conference last month, as proof of the government's commitment to cutting red tape.
The Incorporated Society of British Advertisers (ISBA) was not available for comment on the decision.