Mumbai, Sept. 17 -- The Reserve Bank of India's latest FAQs on non-banking financial companies (NBFCs) may have further weakened Tata Trusts' efforts to keep Tata Sons private, clarifying rules that underpin the central bank's decision to reject the holding company's application to surrender its regulatory registration and avoid a stock-market listing.

Tata Sons is registered with the RBI as a "core investment company" (CIC) - a category for holding companies that mainly invest in their own group's businesses. Large CICs, known as "upper-layer" NBFCs, are required to list on the stock exchange. Tata Sons had asked the RBI to let it exit this category entirely, arguing that since it had repaid more than Rs.20,000 crore in debt and was now...