The commission said the institute had "indirectly" fixed the prices of services provided by estate agents, depriving consumers of competitive prices.
The institute recommends fees for estate agents' services by publishing a tariff book for use by its members.
The book suggests minimum fees, hourly rates and sales commissions to be charged by estate agents (who are members of the body) for property administration services, sales of immovable property, sales of businesses and negotiating leases.
The tariff book recommends a 7.5% commission on residential property sales, which has become a benchmark in the real estate industry, said a statement from the commission on Friday.
Menzi Simelane, the head of the Competition Commission, says that, because of the book prices, competition had become non-existent in the industry.