The Serious Fraud Investigation Office (SFIO) is probing three companies - Ruchi Soya, Sterling Biotech and Kanishk Gold - that are already under the regulatory scanner for loan defaults, according to an official source. The Corporate Affairs Ministry has ordered investigation by SFIO against the three firms for alleged financial irregularities, the source said. In recent months, many companies and individuals, including those related to diamond merchants Nirav Modi and his uncle Mehul Choksi - the alleged kingpins behind the Rs 13,000 crore fraud at Punjab National Bank - have come under the SFIO lens. Ruchi Soya did not respond to a query seeking comments on the SFIO probe while Sterling Biotech and Kanishk Gold could not be immediately contacted. The SFIO, which also has powers to arrest people, mainly investigates violations under the Companies Act. Leading edible oil firm Ruchi Soya Industries is under insolvency proceedings. The company, which owns brands such as Nutrela, Mahakosh, Sunrich and Ruchi Gold, has a total debt of around Rs 12,000 crore. Gujarat-based pharmaceutical company Sterlite Biotech and Chennai-based jewellery firm Kanishk Gold are already being probed by the CBI with respect to default in loan payments. All the three firms have defaulted in paying back bank loans. Among other entities, SFIO is investigating 107 companies and seven Limited Liability Partnerships linked to Modi-Choksi groups with regard to PNB scam. As part of larger efforts to curb illicit fund flows, the government has been cracking the whip on shell companies and defaulting entities, among others.