Police in India are searching the premises of five companies which allegedly misrepresented facts before being allocated the coalfields.
Government officials and company employees are also being investigated, the BBC reports.
Government auditors recently said India lost $US33 billion selling coalfields cheaply between 2006 and 2009.
The raids come as the government rejected opposition demands to cancel the sale of the coalfields.
Parliament has been deadlocked over demands by the opposition Bharatiya Janata Party (BJP) that the government should cancel the sale and order an independent probe into the matter.
Although the report by government auditors does not mention Prime Minister Manmohan Singh, BJP leaders say he must step down as he was heading the coal ministry at the time of the sale.
Mr Singh denies any wrongdoing and has refused to quit.