Tata Sons IPO News, Sept. 14 -- The Reserve Bank of India (RBI) is said to have rejected Tata Sons Private Limited's plea for a waiver from a regulatory rule requiring it to go public. The Tata Group holding company has resisted a stock exchange listing for years, as this would subject it to tighter regulatory oversight and force it to reveal more of the group's internal dealings. But the pressure has been mounting in recent months.

The Central Bank of India tweaked the definition of shadow lenders in May, reviving the debate on whether Tata Sons could be forced to list. In June, the regulator reaffirmed a framework for identifying systemically important shadow lenders, keeping Tata Sons on the hook.

The latest RBI missive makes it even...