CBI sources said the agency has started these inquiries for alleged duty evasion in the exports of 7.28 lakh metric tonnes of iron ore from Kolkata during 2008-11.
They said some customs officials are also under the scanner of the agency.
The sources refused to share details of Chhattisgarh based business groups which have been named as it is still the initial stage and disclosure of the names could hamper further investigations.
The sources said rates of iron ore for consumption in domestic market are less because of relaxation in duty whereas for exports these are on higher side.