New Delhi, Sept. 14 -- The Reserve Bank of India's decision to reject Tata Sons Pvt. Ltd.'s request to remain private has opened a new chapter in the long-running listing saga.

Tata Trusts, which owns 65.9% of Tata Sons, has consistently opposed a listing, and is now expected to challenge the banking regulator in court. The decision comes just days before Tata Sons' 17 September board meeting, where the group's options are likely to be discussed.

At the same time, the stakes are high for Shapoorji Pallonji Group, which owns 18.37% of Tata Sons. A listing could make its prized but illiquid holding easier to monetise and give the debt-laden group a market-based valuation. But the timing is a problem. The SP Group faces near-term repayment...