Federal officials investigating coalfield contracts raided homes and offices in 10 cities across India today.
The Central Bureau of Investigation (CBI) has filed cases against five companies and charged a number of officials with criminal conspiracy, cheating and intention to commit a crime.
No arrests have yet been made although it was reported that documents have been seized.
The companies operate in the main coal-producing states of eastern India.
The CBI had already started looking into the awarding of coalfields when in August the state auditor questioned the lack of competitive bidding for the sites, which are potentially worth billions of pounds.