National Stock Exchange of India Ltd (NSE) and BSE Ltd have written to some listed companies in the Tata group seeking a secretarial audit by their audit committees, four people with direct knowledge of the matter said, including two exchange officials.Sebi itself is examining whether the Tata companies have violated any provisions of the Sebi Act, particularly those relating to listing norms and insider trading rules.A day after Mistry’s letter became public, NSE wrote to Indian Hotels Co. Ltd, Tata Motors Ltd, Tata Steel Ltd, Tata Power Co. Ltd and Tata Teleservices (Maharashtra) Ltd—companies that were referred to as legacy hotspots in Mistry’s letter—seeking clarifications.The companies replied to the exchanges stating that they have made full disclosures of material events.Sebi did not respond to an email seeking comment.In an email, a Tata Sons spokesperson said that the matter concerns group companies and not Tata Sons.